COMPUTER SCIENCE WITH PYTHON
CBSE New Syllabus(Session-2023-24)
CHAPTER NO – 3
File handling
Unit-1 (Computational Thinking and Programming-2)
Need for a data file
Need for a data file :-
Need for a data file :•
To Store data in organized manner
•
To store data permanently
•
To access data faster
•
To Search data faster
•
To easily modify data later on
Unit-1 (Computational Thinking and Programming-2)
File Handling
File: A file is a sequence of bytes on the
disk/permanent storage where a group of related
data is stored. File is created for permanent
storage of data.
File handling: in Python enables us to create,
update, read, and delete the files stored on the
file system through our python program. The
following operations can be performed on a file.
In programming, Sometimes, it is not enough to
only display the data on the console. Those data
are to be retrieved later on, then the concept of file
handling comes. It is impossible to recover the
programmatically generated data again and again.
However, if we need to do so, we may store it onto
the file system which is not volatile and can be
accessed every time. Here, comes the need of file
handling in Python.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Types of File
In Python, File Handling consists of
following three steps:
Open the file & Process file perform
read or write operation,
Close the file.
There are three types of files:
Text Files :- A file whose contents can be viewed using a text
editor is called a text file. A text file is simply a sequence of
ASCII or Unicode characters. Python programs, contents
written in text editors are some of the example of text
files.e.g. .txt,.rtf,.csv etc.
Binary Files :- A binary file stores the data in the same way as
as stored in the memory. The .exe files,mp3 file, image files,
word documents are some of the examples of binary files.
we can’t read a binary file using a text editor.e.g. .bmp,.cdr
etc.
CSV Files:- A Comma Separated Values (CSV) file is a plain
text file that contains a list of data. These files are often used
for exchanging data between different applications. For
example, databases and contact managers often support CSV
files.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Types of File
File Handling :
Types of File
Text File
Its Bits represent character.
Binary File
Its Bits represent a custom data.
Less prone to get corrupt
as change reflects as soon
as made and can be
undone.
Can easily get corrupted, corrupt on even
single bit change
Store only plain text in a file.
Widely used file format and can
be opened in any
text editor.
Mostly .txt,.rtf are used as
extensions to text files.
Can store different types of data
(audio, text,image) in a single
file.
Developed for an application and can be
opened
in that application only.
Can have any application defined extension.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Opening and Closing Files
File Handling :
Opening and Closing Files
Opening and Closing Files :To perform file operation ,it must be opened first then after
reading,writing, editing operation can be performed. To create any new
file then too it must be opened. On opening of any file ,a file relevant
structure is created in memory as well as memory space is created to
store contents.
Once we are done working with the file, we should close the file. Closing
a file releases valuable system resources. In case we forgot to close the
file, Python automatically close the file when program ends or file
object is no longer referenced in the program. However, if our program
is large and we are reading or writing multiple files that can take
significant amount of resource on the system. If we keep opening new
files carelessly, we could run out of resources. So be a good programmer
, close the file as soon as all task are done with it.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Open Function
File Handling : - Open Function
Before any reading or writing operation of any
file, it must be opened first of all.
Python provide built in function open() for it. On
calling of this function creates file object for file
operations.
Open Function :Syntax
file object = open(<file_name>, <access_mode>,
< buffering>)file_name = name of the file
,enclosed in double quotes.
access_mode= Determines the what kind of
operations can be performed with file, like read,
write etc.
Buffering = for no buffering set it to 0. For line
buffering set it to 1. If it is greater than 1, then it
is buffer size. If it is negative then buffer size is
system default.
Unit-1 (Computational Thinking and Programming-2)
File Handling :Opening & closing files
File Handling :
Opening & closing files
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Open Function
File Handling :
access modes
S.No.
Mode & Description
1
r - reading only.Sets file pointer at beginning of the file . This is the default mode.
2
rb – same as r mode but with binary file
3
r+ - both reading and writing. The file pointer placed at the beginning of the file.
4
rb+ - same as r+ mode but with binary file
5
w - writing only. Overwrites the file if the file exists. If not, creates a new file for writing.
6
wb – same as w mode but with binary file.
7
w+ - both writing and reading. Overwrites . If no file exist, creates a new file for R & W.
8
wb+ - same as w+ mode but with binary file.
9
a -for appending. Move file pointer at end of the file.Creates new file for writing,if not exist.
10
ab – same as a but with binary file.
11
a+ - for both appending and reading. Move file pointer at end. If the file does not exist, it
creates a new file for reading and writing.
12
ab+ - same as a+ mode but with binary mode.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Basic Text file operations
File Handling : Basic Text file operations
•
Open (filename – absolute or relative path, mode)
•
Close a text file
•
Reading / Writing data
•
Manipulation of data
•
Appending data into a text file
Unit-1 (Computational Thinking and Programming-2)
File Handling: Reading a file
File Handling :
Reading a file
Unit-1 (Computational Thinking and Programming-2)
File Handling: Reading a file
File Handling :
Reading a file
Unit-1 (Computational Thinking and Programming-2)
File Handling :writing to a file
File Handling :
Writing to a file
Unit-1 (Computational Thinking and Programming-2)
File Handling :writing to a file
File Handling :
Writing to a file
Unit-1 (Computational Thinking and Programming-2)
File Handling :writing to a file
File Handling :
Writing to a file
Unit-1 (Computational Thinking and Programming-2)
File Handling : Appending in a file
File Handling :
Appending in a file
Unit-1 (Computational Thinking and Programming-2)
File Handling : -writing user input to the file
File Handling :
writing user input to the file
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Basic Text file operations
File Handling :
Basic Text file operations
e.g.
program import os print(os.getcwd())
os.mkdir("newdir")
os.chdir("newdir") print(os.getcwd())
Methods of os module
Before Starting file operation following methods must be
learn by a programmer to perform file system related
methods available in os module(standard module) which
can be used during file operations.
The rename() method used to rename the file.
Syntax:
os.rename(current_file_name,new_file_name)
The remove() method to delete file.
Syntax : os.remove(file_name)
The mkdir() method of the os module to create directories
in the current directory.
Syntax: os.mkdir("newdir")
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Basic Text file operations
File Handling :
Basic Text file operations
The chdir() method to change the current directory.
Syntax os.chdir("newdir")
The getcwd() method displays the current directory.
Syntax os.getcwd()
The rmdir() method deletes the directory.
Syntax os.rmdir('dirname')
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Absolute Path vs Relative Path
File Handling :
Absolute Path vs Relative Path
Absolute Path vs Relative Path :One must be familiar with absolute & relative path
before starting file related operations.
The absolute path is the full path to some place on your
computer. The relative path is the path to some file
with respect to your current working directory (CWD).
For example:
Absolute path: C:/users/admin/docs/staff.txt
If CWD is C:/users/admin/,
then the relative path to staff.txt would be:
docs/staff.txt
Note, CWD + relative path = absolute path.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Absolute Path vs Relative Path
e.g. program
File Handling :
Absolute Path vs Relative Path
import os
print(os.getcwd())
os.mkdir("newdir1")
os.chdir("newdir1")
print(os.getcwd())
my_absolute_dirpath=os.path.abspath(os.path.dirname ( file ))
print(my_absolute_dirpath)
Unit-1 (Computational Thinking and Programming-2)
File Handling : - File object attributes
File Handling :
File object attributes
demofile.txt
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
open a text file
closed: It returns true if the file is closed and false when the file is
open. To open the file, use the built-in open() function.
The open() function returns a file object, which has
a read() method for reading the content of the file:
encoding: Encoding used for byte string conversion.
mode: Returns file opening mode
name: Returns the name of the file which file object holds.
newlines: Returns “\r”, “\n”, “\r\n”, None or a tuple containing all
the newline types seen.
Output:e.g. Program
f = open("demofile.txt", "r") Hello! Welcome to demofile.txt
print(f.read())
This file is for testing purposes.
Good Luck!
Unit-1 (Computational Thinking and Programming-2)
File Handling : - File object attributes
File Handling :
File object attributes
demofile.txt
Hello! Welcome todemofile.txt
This file is for testing purposes.
Good Luck!
open a text file
If the file is located in a different location, you will have to
specify the file path, like this:
f = open("D:\\myfiles\welcome.txt", "r")
print(f.read())
Output:f = open("D:\\myfiles\welcome.txt",
"r")​print(f.read())​
Welcome to this text file!
This file is located in a folder named "myfiles",
on the D drive.
Good Luck!
Unit-1 (Computational Thinking and Programming-2)
File Handling : - File object attributes
open a text file
File Handling :
File object attributes
demofile.txt
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
readline()
Read one line of the file:
e.g. program
f = open("demofile.txt", "r")
Output:print(f.readline())
Hello! Welcome to demofile.txt
Read two lines of the file:
e.g. program
Output:f = open("demofile.txt", "r") Hello! Welcome to demofile.txt
print(f.readline())
This file is for testing purposes.
print(f.readline())
Unit-1 (Computational Thinking and Programming-2)
File Handling : - File object attributes
open a text file
File Handling :
File object attributes
demofile.txt
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
Loop through the file line by line:
e.g. program
f = open("demofile.txt", "r")
for x in f:
print(x)
Output:Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
Unit-1 (Computational Thinking and Programming-2)
File Handling : - File object attributes
File Handling :
File object attributes
demofile.txt
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
open a text file
Read Only Parts of the File
By default the read() method returns the whole text, but you can
also specify how many characters you want to return:
Return the 5 first characters of the file:
e.g. program
f = open("demofile.txt", "r")
print(f.read(5))
Output:-
Hello
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Close a text file
File Handling :
File object attributes
demofile.txt
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
Close a text file :close(): Used to close an open file. After using this method,
an opened file will be closed and a closed file cannot be
read or written any more. Close the file when you are finish
with it:
e.g. program
f = open("demofile.txt", "r")
print(f.readline())
f.close()
Output:
Hello! Welcome to demofile.txt
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Read/write text file
File Handling :
File object attributes
demofile.txt
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
Read/write text file
The write() Method
It writes the contents to the file in the form of string. It does
not return value. Due to buffering, the string may not actually
show up in the file until the flush() or close() method is called.
The read() Method
It reads the entire file and returns it contents in the form of a
string. Reads at most size bytes or less if end of file occurs. If
size not mentioned then read the entire file contents.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Read/write text file
File Handling :
File object attributes
Python Delete File
Python Delete File
Delete a File
To delete a file, you must import the OS module,
and run its os.remove() function:
Example
Remove the file "demofile.txt":
import os
os.remove("demofile.txt")
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Read/write text file
File Handling :
File object attributes
Python Delete File
Python Delete File
Check if File exist:
To avoid getting an error, you might want to check if the file
exists before you try to delete it:
Example
Check if file exists, then delete it:
import os
if os.path.exists("demofile.txt"):
os.remove("demofile.txt")
else:
print("The file does not exist")
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Read/write text file
File Handling :
File object attributes
Python Delete Folder
Delete Folder
To delete an entire folder, use the os.rmdir() method:
Example
Remove the folder "myfolder":
import os
os.rmdir("myfolder")
Note: You can only remove empty folders
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Read/write text file
File Handling :
File object
attributes
Python Delete File
Python Delete File
Delete a File
To delete a file, you must import the OS module, and run its
os.remove() function:
Example
Remove the file "demofile.txt":
import os
os.remove("demofile.txt")
Check if File exist:
To avoid getting an error, you might want to check if the file
exists before you try to delete it:
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Read/write text file
File Handling :
File object attributes
Create a New File
Create a New File
To create a new file in Python, use the open() method, with one of the
following parameters:
"x" - Create - will create a file, returns an error if the file exist
"a" - Append - will create a file if the specified file does not exist
"w" - Write - will create a file if the specified file does not exist
Example:
Create a file called "myfile.txt":
f = open("myfile.txt", "x")
Result: a new empty file is created!
Example:
Create a new file if it does not exist:
f = open("myfile.txt", "w")
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Read/write text file
File Handling :
File object
attributes
demofile.txt
Hello!
Welcome
to demofile.txt
This file is for
testing purposes.
Good Luck!
write() ,read() Method based program
Write to an Existing File
To write to an existing file, you must add a parameter to
the open() function:
"a" - Append - will append to the end of the file
"w" - Write - will overwrite any existing content
Open the file "demofile2.txt" and append content to the file:
e.g program
f = open("demofile2.txt", "a")
f.write("Now the file has more content!")
f.close()
#open and read the file after the appending:
f = open("demofile2.txt", "r") Output:Hello! Welcome to demofile2.txt
print(f.read())
This file is for testing purposes.
Good Luck!Now the file has more content!
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Read Text file
readline([size]) method:
read no of characters from
file if size is mentioned till
eof.
read line till new line
character. returns empty
string on EOF.
Read Text file
e.g. program
f = open("a.txt", 'w')
line1 = 'Welcome to python'
f.write(line1)
line2="\nRegularly visit python"
f.write(line2)
f.close()
f = open("a.txt", 'r')
text = f.readline()
print(text)
OUTPUT
text = f.readline()
Welcome to python Regularly visit
print(text)
python
f.close()
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Read Text file
readlines([size]) method:
read no of lines from file if size
is mentioned or all contents if
size is not mentioned.
Read Text file
e.g.program
f = open("a.txt", 'w')
line1 = 'Welcome to python.in'
f.write(line1)
line2="\nRegularly visit python.in"
f.write(line2)
OUTPUT
f.close()
['Welcome to python.in\n']
f = open("a.txt", 'r')
NOTE – READ ONLY ONE
text = f.readlines(1) LINE IN ABOVE PROGRAM.
print(text)
f.close()
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Read Text file
File Handling :
read Text file Iterating over lines in
a file
Iterating over lines in a
file e.g.program
f = open("a.txt", 'w')
line1 = 'Welcome to python.in'
f.write(line1)
line2="\nRegularly visit python.in"
f.write(line2)
f.close()
f = open("a.txt", 'r')\
for text in f.readlines():
print(text)
f.close()
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Read Text file
File Handling :
read text file processing every
word in a file
Processing Every Word in a File
f =open("a.txt", 'w')
line1 = 'Welcome to python.in' f.write(line1)
line2="\nRegularly visit python.in"
f.write(line2)
f.close()
f = open("a.txt", 'r')
for text in f.readlines():
for word in text.split( ):
print(word)
f.close()
OUTPUT
Welcome to python.in Regularly visit python.in
Unit-1 (Computational Thinking and Programming-2)
File Handling : -rename method( )
File Handling :
rename method( )
rename( ) method:rename() method in Python is used to rename a file or
directory. This method renames a source file/ directory to specified
destination file/directory.
Steps to Rename File in Python
To rename a file, Please follow these steps:
Find the path of a file to rename
To rename a file, we need its path. The path is the location of the file on the
disk.
An absolute path contains the complete directory list required to locate the
file.
A relative path contains the current directory and then the file name.
Decide a new name
Save an old name and a new name in two separate variables.
old_name = 'details.txt'
new_name = 'new_details.txt'
Unit-1 (Computational Thinking and Programming-2)
File Handling : -rename method( )
Example: Renaming a file in Python
In this example, we are renaming “detail.txt” to
Use rename() method of an
OS module
“new_details.txt”.
Use the os.rename() method
import os
to rename a file in a folder.
# Absolute path of a file
Pass both the old name and
old_name = r"E:\demos\files\reports\details.txt"
a new name to the
new_name = r"E:\demos\files\reports\new_details.txt"
os.rename
# Renaming the file
(old_name, new_name)
os.rename(old_name, new_name)
function to rename a file.
Output: Before rename file After renaming a file
Unit-1 (Computational Thinking and Programming-2)
File Handling : -remove method( )
remove method( ):
The remove() method takes a
single element as an argument
and removes it from the list. If
the element doesn't exist, it
throws ValueError:
Example
Remove the "banana" element of the fruit
list:
fruits = ['apple', 'banana', 'cherry']
fruits.remove("banana")
Output:
['apple', 'cherry']
Unit-1 (Computational Thinking and Programming-2)
File Handling : -Flush method( )
Flush method( ) :
Python file method flush() flushes the
internal buffer, like stdio's fflush. This
may be a no-op on some file-like objects.
Python automatically flushes the files
when closing them. But you may want to
flush the data before closing any file.
!/usr/bin/python
# Open a file
fo = open("foo.txt", "wb")
print "Name of the file: ", fo.name
# Here it does nothing, but you can call it with
read operation.
fo.flush()
# Close opend file
fo.close()
When we run above program, it produces
following result −
Name of the file: foo.txt
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Getting & Resetting the Files Position
Getting & Resetting the Files Position
Getting & Resetting the Files Position:
The tell() method
The seek (offset [, from]) method
The tell() method of python tells us the current
position within the file,
where as the seek (offset [, from]) method
changes the current file position. If from is 0, the
beginning of the file to seek. If it is set to 1, the
current position is used . If it is set to 2 then the
end of the file would be taken as seek position.
The offset argument indicates the number of
bytes to be moved.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Getting & Resetting the Files Position
The tell() method:
The tell() method returns the current file
position in a file stream.
demofile.txt
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
Return the current file position after reading the
first line:
e.g:program
f = open("demofile.txt", "r")
print(f.readline())
print(f.tell())
Output:Hello! Welcome to demofile.txt
32
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Getting & Resetting the Files Position
tell(): In python programming, within file
handling concept tell() function is used to
get the actual position of file object. By
file object we mean a cursor. And it’s
cursor, who decides from where data has
to be read or written in a file.
Syntax:
f.tell()
#here f is file handler or file object
Explanation: We opened “test.txt” file in read mode. If
file opened in read mode than by default file object or
file pointer at beginning ie. 0 position. Hence our
output is 0. You can also see in above image (data
written in text file) highlighted in yellow that pointer
is at beginning.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Getting & Resetting the Files Position
seek() method : The seek() method sets
the current file position in a file stream.
The seek() method also returns the new
postion. demofile.txt
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
You can change the current file position with the seek()
method.
Change the current file position to 4, and return the
rest of the line:
e.g:program
f = open("demofile.txt", "r")
f.seek(4)
print(f.readline())
Output:o! Welcome to demofile.txt
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Getting & Resetting the Files Position
seek()method:
The seek() method sets the current file
position in a file stream.
The seek() method also returns the new
postion. demofile.txt
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
You can change the current file position with the seek()
method.
Change the current file position to 4, and return the
rest of the line:
Return the new position:
e.g:program
f = open("demofile.txt", "r")
print(f.seek(4))
Output:4
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Getting & Resetting the Files Position
seek():
In python programming, within file
handling concept seek() function is used
to shift/change the position of file object
to required position. By file object we
mean a cursor. And it’s cursor, who
decides from where data has to be read or
write in a file.
Syntax:
f.seek(offset)
#here f is file handler or file object
#here offset is postions to move forward
Explanation: We opened “test.txt” file in read mode. If file
opened in read mode than by default file object or file pointer
at beginning ie. 0 position. But here we used seek() function
and set its position to 6. It means now our pointer has gone to
sixth position, if we start reading then it will start reading
from sixth character. Hence our output is “there how are
you?”. You can also see in above image (data written in text
file) highlighted in yellow that “hello” is skipped because
pointer is moved to sixth character using seek() function.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Modify a Text file
Modify a Text file:
Modify a Text file:
There is no way to insert into the middle
of a file without re-writing it. We can
append to a file or overwrite part of it
using seek but if we want to add text at
the beginning or the middle, we'll have
to rewrite it.
It is an operating system task, not a Python task. It is the
same in all languages.
What we usually do for modification is read from the
file, make the modifications and write it out to a new
file called temp.txt or something like that. This is better
than reading the whole file into memory because the
file may be too large for that. Once the temporary file is
completed, rename it the same as the original file. This
is a good, safe way to do it because if the file write
crashes or aborts for any reason in between, we still
have our untouched original file.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Modify a Text file
replace string in the same File
fin = open("dummy.txt", "rt")
data = fin.read()
data = data.replace(‘my', ‘your')
fin.close()
fin = open("dummy.txt", wt")
fin.write(data)
fin.close()
What have we done here?
Open file dummy.txt in read text mode rt.
fin.read() reads whole text in dummy.txt to the
variable data.
data.replace() replaces all the occurrences of my
with your in the whole text. fin.close() closes the
input file dummy.txt.
In the last three lines, we are opening dummy.txt in
write text wt mode and writing the data to
dummy.txt n replace mode. Finally closing the file
dummy.txt.
Note :- above program is suitable for file with small
size.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Modify a Text file
import os
f=open("d:\\a.txt","r")
g=open("d:\\c.txt","w")
for text in f.readlines():
text=text.replace('my','your')
g.write(text)
f.close()
g.close() os.remove("d:\\a.txt")
os.rename("d:\\c.txt","d:\\a.txt")
print("file contents modified")
Note- above program is suitable for large file.Here line
by line is being read from a.txt file in text string and
text string been replaced ‘my’ with ‘your’ through
replace() method.
Each text is written in c.txt file then close both files
,remove old file a.txt through remove method of os
module and rename c.txt(temporary file) file with
a.txt file.
After execution of above program all occurances of
‘my’ will be replaced with ‘your’.For testing of above
program create a.txt file in d: drive with some
substring as ‘my’.Run above program and check
changes.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Append content to a Text file
Append Only (‘a’):
Open the file for writing.
Append and Read (‘a+’):
Open the file for reading and
writing.
# append from new line
file1 = open("myfile.txt", "w")
L = ["This is Delhi \n", "This is Paris \n", "This is London"]
file1.writelines(L)
Output:
file1.close()
# Append-adds at last
Output of Readlines after appending
# append mode
file1 = open("myfile.txt", "a") This is Delhi
# writing newline character This is Paris
This is London
file1.write("\n")
Today Tomorrow
file1.write("Today")
# without newline character
file1.write("Tomorrow")
file1 = open("myfile.txt", "r")
print("Output of Readlines after appending")
print(file1.read())
print()
file1.close()
Unit-1 (Computational Thinking and Programming-2)
Standard Input, Output, and Error
Standard Input, Output, and Error:The
interpreter provides three standard file
objects, known as standard input,
standard output, and standard error,
which are available in the sys module as
sys.stdin, sys.stdout, and sys.stderr,
respectively.
stdin is a file object corresponding to the stream of
input characters supplied to the interpreter. stdout
is the file object that receives output produced by
print.stderr is a file that receives error messages.
More often than not, stdin is mapped to the user’s
keyboard, whereas stdout and stderr produce text
onscreen.
The methods described in the preceding section
can be used to perform raw I/O with the user. For
example, the following function reads a line of
input from standard input:
def gets(): text ...
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Operations in Binary file
Operations in Binary file
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Write and read a Binary file
Write and read a Binary file
Example: Write to a Binary File Copy
f=open("binfile.bin","wb")
num=[5, 10, 15, 20, 25]
arr=bytearray(num)
f.write(arr)
f.close()
Writing to a Binary File
The open() function opens a file in text format by
default. To open a file in binary format, add 'b' to the
mode parameter. Hence the "rb" mode opens the file
in binary format for reading, while the "wb" mode
opens the file in binary format for writing. Unlike text
files, binary files are not human-readable. When
opened using any text editor, the data is
unrecognizable.
The following code stores a list of numbers in a binary
file. The list is first converted in a byte array before
writing. The built-in function bytearray() returns a byte
representation of the object.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Binary file Operation using pickle module
Binary file Operation using pickle module :
The problem with the approach of
previous slide comes from the fact that it
is not very easy to use when we want to
write several objects into the binary file.
Binary file Operation using pickle module :For instance, consider what we would have to do if we
wished to write string, integer and perhaps even the
contents of a list or dictionary into the file. How would
we read the contents of this file later?
This is not a trivial task, especially if some of the objects
can have variable lengths.
Fortunately, Python has a module which does this work
for us and is extremely easy to use. This module is
called pickle; it provides us with the ability to serialize
and deserialize objects, i.e., to convert objects into
bitstreams which can be stored into files and later be
used to reconstruct the original objects.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Binary file Operation using pickle module
Binary file Operation using pickle module :
Binary file Operation using pickle module :pickle.dump() function is used to store the object data
to the file. It takes 3 arguments.First argument is the
object that we want to store. The second argument is
the file object we get by opening the desired file in
write-binary (wb) mode. And the third argument is the
key-value argument. This argument defines the protocol.
There are two type of protocol –
pickle.HIGHEST_PROTOCOL and
pickle.DEFAULT_PROTOCOL.
Pickle.load() function is used to retrieve pickled data.The
steps are quite simple. We have to use pickle.load()
function to do that. The primary argument of pickle
load function is the file object that you get by opening
the file in read-binary (rb) mode.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Binary file Operation using pickle module
Pickling:
The process of converting the structure
(lists and dictionary etc.) into a byte
stream just before writing to the file. This
is also called as object serialization.
dump() function: We use dump() method to
perform pickling operation on our Binary Files. It
returns the object representation in byte mode.
The dump() method belongs to pickle module.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Binary file Operation using pickle module
#pickling_in_python
import pickle
pickle.dump(object,file)
#Example_pickling_in_python
import pickle
def write():
file = open("binary.dat",'wb')
x = [1,2,3,4,5] #data we wrote in file
pickle.dump(x,file)
file.close()
write()
Output data stored in file:
Note: Hence we can observe the output that what data
we wrote and what was inserted in our file. Actually data
stored is correct but it has been stored in binary format
which is not readable by humans.
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Binary file Operation using pickle module
Unpickling:
The reverse conversion of byte
stream back to the structure (lists,
dictionary, tuples etc.) refers to
unpickling.
Basically it is the reverse operation of
pickling. This is also called deserialization.
We use load() method for unpickling.
This load() function/method also
belongs to pickle module.
load() function:
In pickle module, load() function is used to
read data from a binary file or file object
Unit-1 (Computational Thinking and Programming-2)
File Handling : - Binary file Operation using pickle module
Syntax:
#Syntax_unpickling_in_python
import pickle
pickle.load(file)
#Example_unpickling
import pickle
def read():
file = open("binary.dat",'rb')
data = pickle.load(file)
file.close()
print(data)
read()
Output:[1, 2, 3, 4, 5]
Unit-1 (Computational Thinking and Programming-2)
File Handling : Search record in a Binary file
Here value of r to be searched will be
compared with rollno value of file in
each iteration / next record and if
matches then relevant data will be
shown and flag will be set to true other
wise it will remain False and 'No record
found message will be displayed'
Search record in a Binary file-pickle module
def check():
import pickle
f = open('d:/student.dat','rb')
flag = False
r=int(input(“Enter rollno to be searched”))
while True:
try:
rec = pickle.load(f)
if rec['Rollno'] == r:
print('Roll Num:',rec['Rollno'])
print('Name:',rec['Name'])
print('Marks:',rec['Marks'])
flag = True
except EOFerror:
break
if flag == False:
print('No Records found')
f.close()
Unit-1 (Computational Thinking and Programming-2)
File Handling : Update record of a Binary file
Here we are reading all records from binary file
and storing those in reclst list then update
relevant roll no /marks data in reclst list and
create /replace student.dat file with all data of
reclst.
If large data are in student.dat file then it’s
alternative way can be using temporary file
creation with corrected data then using os
module for remove and rename method
(just similar to modification of text file)
Update record of a Binary file-pickle module
import os
import sys
import file input
f = open('d:/student.dat','rb') reclst = []
r=int(input(“enter roll no to be updated”))
m=int(input(“enter correct marks”))
while True:
try:
rec = pickle.load(f) reclst.append(rec)
except EOFError:
break
f.close()
for i in range (len(reclst)):
if reclst[i]['Rollno']==r:
reclst[i]['Marks'] = m
f = open('d:/student.dat','wb') for x in reclst:
pickle.dump(x,f)
f.close()
Unit-1 (Computational Thinking and Programming-2)
File Handling : Delete record of a Binary file
Here we are reading all records from binary file and
storing those in reclst list then write all records
except matching roll no
(with the help of
continue statement) in
student.dat file.
Due to wb mode old data will be removed. If large
data are in student.dat file then It’s alternative way
can be then It’s alternative way can be for remove
and rename method
(just similar to deletion from text file)
Delete record of a Binary file
pickle module
import os
f = open('d:/student.dat','rb')
reclst = []
r=int(input(“enter rollno to deleted))
while True:
try:
rec = pickle.load(f) reclst.append(rec)
except EOFError: break
f.close()
f = open('d:/student.dat','wb')
for x in reclst:
if x['Rollno']==r:
continue
pickle.dump(x,f)
f.close()
Unit-1 (Computational Thinking and Programming-2)
File Handling : CSV FILE (Comma separated value)
CSV FILE
(Comma separated value):CSV (Comma Separated Values) is a file
format for data storage which looks like a
text file. The information is organized with
one record on each line and each field is
separated by comma.
CSV File Characteristics
One line for each record
Comma separated fields
Space-characters adjacent to commas are ignored
Fields with in-built commas are separated by
double quote characters.
When Use CSV?
When data has a strict tabular structure
To transfer large database between programs
To import and export data to office applications,
Qedoc modules
To store, manage and modify shopping cart
catalogue
Unit-1 (Computational Thinking and Programming-2)
File Handling : CSV Advantages
CSV FILE
(Comma separated value) Advantages :-
CSV FILE (Comma separated value) Advantages :CSV is faster to handle
CSV is smaller in size
CSV is easy to generate
CSV is human readable and easy to edit manually
CSV is simple to implement and parse
CSV is processed by almost all existing applications CSV
Disadvantages
No standard way to represent binary data
There is no distinction between text and numeric values
Poor support of special characters and control characters
CSV allows to move most basic data only. Complex
configurations cannot be imported and exported this way
Problems with importing CSV into SQL (no distinction
between NULL and quotes)
Unit-1 (Computational Thinking and Programming-2)
File Handling : Write / Read CSV FILE
using open() method which create new File like
object.
Through csv.writer() method ,we create writer
object to call writerow() method to write objects.
Similarly for reading ,we open the file in ‘r’ mode
and create new File like object,
further we create newfilereader object using
csv.reader()method to read each row of the file.
Three file opening modes are there ‘w’,’r’,’a’. ‘a’ for
append After file operation close ,opened file
using close() method.
Write / Read CSV FILE
Writing and reading operation from text file is very easy. First
of all we have to import csv module for file operation/method
call. For writing ,we open file in ‘w’ writing
import csv
#csv file writing code
with open('d:\\a.csv','w') as newFile:
newFileWriter = csv.writer(newFile)
newFileWriter.writerow(['user_id','beneficiary'])
newFileWriter.writerow([1,'xyz'])
newFileWriter.writerow([2,'pqr'])
newFile.close()
#csv file reading code
with open('d:\\a.csv','r') as newFile:
newFileReader = csv.reader(newFile)
for row in newFileReader:
print (row)
newFile.close()
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.What is the difference between "w" and "a" modes?
Ans."w" mode :- If file exists, python will delete all data of the file.
"a" mode :- If file exists, the data in the file is retained and new data being written
will be appended to end.
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.How is file open() function different from close() function ?
Ans. open () function is a built in function while close () function is a method
used with file handle object.
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.What role is played by file modes in file operations?
Describe the various file mode constants and their meanings.
Ans. File mode refers to how the file will be used once it's opened.There are
three types of file modes:(1) read mode :- It will read data of file according to program.
(2) write mode :- Python delete all data and write new data according to user.
(3) append mode :- The data in the file is retained and new data being written
will be appended to end.
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.What is following code doing?
file = open("contacts.csv", "a")
name = input("Please enter name.")
phno = input("Please enter phone number.")
file.write (name + "," + phone + "\n")
Ans.It will take data from user and write data in file ‘contacts.csv’
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.Write a method in python to write multiple line of text content into a text file
mylife.txt line.
Ans. file = open("mylife.txt", "w")
l = []
while True:
data = input("Enter the contents otherwise, Enter ""exit"" for stop the program :")
if data == 'exit':
break
else :
l = l + [data + '\n']
file.writelines (l)
file.close ()
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.Write a program to count the number of upper- case alphabets present in a text file
"Article.txt".
Ans. count = 0
file = open("pathwala.txt","r")
sen = file.read()
for i in range ( len(sen) ) :
if sen[ i ].isupper() :
count += 1
print("Number of upper case alphabet : ", count)
file.close()
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.Write a program to count the words "to" and "the" present in a text file "Poem.txt".
Ans. to_no = 0
the_no = 0
file = open("Poem.txt", "r")
lst = file.readlines()
for i in lst :
word = i.split()
for j in word :
if j == "to" :
to_no += 1
elif j == "the" or j == "The" :
the_no += 1
print("Number 'to' : " , to_no)
print("Number 'the' : " , the_no)
file.close()
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.Write a program that copies one file to another. Have the program read the file names
from user ?
Ans.file = input("Enter the name of file with its formate : ")
old = open( file , "r")
new = open("New file.txt", "w")
data = old.read()
new.write( data )
print(" Program run successfully ")
old.close()
new.close()
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Board Questions
Q. Write a program in python to replace all word ‘the’ by
another word ‘them’ in a file “poem.txt”.
Ans .
f=open(“poem.txt”)
d=f.read()
d = d.replace(“the”,them”)
f.close()
f=open(“poem.txt”,w”)
f.write(d)
f.close()
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.Write a function search(name) in Python which will display record
of a student from file “school.dat” whose name is passed as an
argument. Structure stored in “school.dat” is in the form of list
containing information like [rollno , name, class, percentage]
Ans.
def search(nm):
f=open(“school.dat”,”rb”)
try:
while True:
d=pickle.load(f)
if d[1].lower()==nm.lower():
print(“Roll Number:”,d[0],”\n”)
print(“Name :”,d[1],”\n”)
print(“Class :”,d[2],”\n”)
print(“Percentage :”,d[3],”\n”)
except:
f.close()
nm=input(“Enter name of the student”)
search(nm)
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.A text file ”PARA txt” contains a paragraph Write a function that searches for
a given character and reports the number of occurrence of the character in the
file.
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.Write a function in Python to count the number of lowercase and uppercase
characters in a textfile “Book, txt”.
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.Write a python code to find the size of the file in bytes, number of lines and number
of words.# reading data from a file and find size, lines, words f=open(“Lines.txt’,’r’)
Unit-1 (Computational Thinking and Programming-2)
Board Questions
Q.What is the difference between Text file and binary file ?