Lecture # 28
Python II
More Python
• Strings and Arrays
• Keyboard I/O (Input/Output)
• File I/O
Jython Strings and Arrays
• If we make the following assignment
s = “Hello”
• What is s?
Jython Strings and Arrays
• If we make the following assignment
s = “Hello”
• What is s?
An array of characters
Jython Strings and Arrays
• If we make the following assignment
s = “Hello”
• What is s?
An array of characters
•What is s[1]?
Jython Strings and Arrays
• If we make the following assignment
s = “Hello”
• What is s?
An array
•What is s[1]?
e
Jython String and Array length
• If we make the following assignment
s = “Hello”
• What is the length of s?
Jython String and Array length
• If we make the following assignment
s = “Hello”
• What is the length of s?
• How do we get the length of s?
Jython String and Array length
• If we make the following assignment
s = “Hello”
• What is the length of s?
• How do we get the length of s?
• len(s)
Try print len(s)
Jython Strings and Arrays
• If we make the following assignment
list = [27, 101, 33]
• What is list?
Jython Strings and Arrays
• If we make the following assignment
list = [27, 101, 33]
• What is list?
An array or list of numbers
Jython Strings and Arrays
• If we make the following assignment
list = [27, 101, 33]
• What is list?
An array or list of numbers
• What is list[2]?
Jython Strings and Arrays
• If we make the following assignment
list = [27, 101, 33]
• What is list?
An array or list of numbers
• What is list[2]?
33
Jython Strings and Arrays
• If we make the following assignment
names = [“Mary”, “Bill”, “Jill”]
• What is names?
Jython Strings and Arrays
• If we make the following assignment
names = [“Mary”, “Bill”, “Jill”]
• What is names?
An array or list of strings
Jython Strings and Arrays
• If we make the following assignment
names = [“Mary”, “Bill”, “Jill”]
• What is names?
An array or list of strings
•What is names[0]?
Jython Strings and Arrays
• If we make the following assignment
names = [“Mary”, “Bill”, “Jill”]
• What is names?
An array or list of strings
•What is names[0]?
Mary
Jython Strings and Arrays
• If we make the following assignment
Big_string = “The quick brown fox jumped over
the lazy dogs.”
• What is Big_string?
Jython Strings and Arrays
• If we make the following assignment
Big_string = “The quick brown fox jumped over
the lazy dogs.”
• What is Big_string?
An array of characters
Jython Strings and Arrays
• If we make the following assignment
Big_string = “The quick brown fox jumped over
the lazy dogs.”
• What is Big_string?
An array of characters
•What is Big_string [7]?
Jython Strings and Arrays
• If we make the following assignment
Big_string = “The quick brown fox jumped over
the lazy dogs.”
• What is Big_string?
An array of characters
•What is Big_string [7]?
c
Jython Keyboard I/O
• To get input from the keyboard and assign
it to a variable:
Jython Keyboard I/O
• To get input from the keyboard and assign
it to a variable:
• fav = raw_input(“What’s your favorite food?: ”)
Jython Keyboard I/O
• To get input from the keyboard and assign
it to a variable:
• fav = raw_input(“What’s your favorite food?: ”)
• What’s your favorite food?: Pizza
input
Jython Keyboard I/O
• To get input from the keyboard and assign
it to a variable:
• fav = raw_input(“What’s your favorite food?: ”)
• What’s your favorite food?: Pizza
• print fav
Pizza
output
input
Jython Keyboard I/O
To produce output using mix of data types:
s = “Hello World!”
r = 1.23456
i=7
print “Mixed Message: %d, %s, %f” % (i,
s, r)
What happens if you don’t use %d, %s, etc.?
Jython File I/O
• Create a text file using Notepad:
Enter a String of text:
“The quick brown fox jumped over the lazy
dogs.”
• Save the file as: Text.txt
Jython File I/O: Reading from files
• Open the file with Python and assign the
file path/name to variable f:
f = open(pickAFile())
• Save the contents of the file in s:
s = f.read()
• Display the contents of the file:
print s
Opening Files
• open(filename, mode)
– filename – text
• absolute path is best: Ex:
”C:/MyFolder/MyPix/photo.jpg”
• relative path - relative to where the program was started
(absolute path is best in JES)
Opening Files
• open(filename, mode)
– mode – text
•
•
•
•
•
•
•
r – open for reading (default)
w – open for writing
a – open for writing, appending to the end of the file
b – binary mode
t – text mode (default)
+ - open file for updating (reading and writing)
combinations: rt, bt, rwt
Jython File I/O: Writing to files
• Open the file with Python and assign the
file path/name to variable f:
f = open(“myfile.txt”,”wt”)
• Write some text to the file:
f.write(“Here is some text.”)
Jython File I/O: Writing to files
• Open the file with Python and assign the
file path/name to variable f:
f = open(“myfile.txt”,”wt”)
• Write some text to the file:
f.write(“Here is some text.”)
f.write(“Here is some more text.\n”)
Jython File I/O: Writing to files
• Open the file with Python and assign the
file path/name to variable f:
f = open(“myfile.txt”,”wt”)
• Write some text to the file:
f.write(“Here is some text.”)
f.write(“Here is some more text.\n”)
f.write(“We’re done.\n\n THE END!”)
Jython File I/O: Writing to files
• Open the file with Python and assign the
file path/name to variable f:
f = open(“myfile.txt”,”wt”)
• Write some text to the file:
f.write(“Here is some text.”)
f.write(“Here is some more text.\n”)
f.write(“We’re done.\n\n THE END!”)
f.close()
Jython File I/O: Writing to files
• Open the file with Python and assign the
file path/name to variable f:
f = open(“myfile.txt”,”wt”)
• Write some text to the file:
f.write(“Here is some text.”)
f.write(“Here is some more text.\n”)
f.write(“We’re done.\n\n THE END!”)
f.close()
f = open(“myfile.txt”,”rt”)
print f.read()
Reading and Writing
• Operations on text files
–
–
–
–
file.read()
file.readline()
file.readlines()
file.write(string)
• It must be a string
– use str(i) function to convert things to strings
– file.close()