Introduction to Python Programming
- Python Programming BasicKnowledge-based Data Discovery
INHA KDD Lab.
Young-Duk Seo
mysid88@inha.ac.kr
2
What is Python?
▪
Python is currently a popular programing language
- Created by Guido van Rossum who is a Dutch programmer, and released in 1991
- Interpreter (Interpreted language or Scripting language)
» code can be executed as soon as it is written
3
Guido van Rossum
(Source: Wiki)
Features of Python
▪
Similar to the English language
- if 4 in [1,2,3,4]: print("There is a 4")
» If 4 is among [1, 2, 3, 4], the “There is a 4” is an output
▪
Easy to learn
- because Python has a simple syntax
▪
An opensource SW
▪
Prototyping with Python can be very quick
- “Life is too short, You need Python.”
4
Basic syntax of Python
▪
Python variable
- String
- Integer
>>> a = "Python"
>>> print(a)
Python
>>> a = 1
>>> b = 2
>>> a + b
3
>>> a = "Python"
>>> a
'Python'
5
Basic syntax of Python
▪
Python conditions
- if
>>> a = 3
>>> if a > 1:
...
print("a is greater than 1")
...
a is greater than 1
❖ The '...' in front of the print statement means that the statement is not finished yet
❖ This space always be indented using the Tab key or 4 spacebar keys
6
Image source: https://wikidocs.net/17684
Editors of Python (Python IDLE)
▪
Python IDLE (Integrated Development and Learning Environment)
IDLE shell window
7
Image source: https://wikidocs.net/17684
Editors of Python
▪
▪
Visual Studio Code
- https://code.visualstudio.com
PyCharm
- http://www.jetbrains.com/pycharm/download
8
Downloading Python
▪
https://www.python.org/
9
Installing Python (Windows)
10
Installing Python (Mac)
11
Installing PyCharm (Windows)
▪
https://www.jetbrains.com/ko-kr/pycharm/download/#section=windows
▪
Community version Download
12
Installing PyCharm (Mac)
▪
https://www.jetbrains.com/ko-kr/pycharm/download/#section=mac
▪
Community version Download
13
Environmental Setting (Windows)
▪
CS101 Library 다운
- https://github.com/cjnam/ice1003/archive/main.zip
14
Hubo library
▪
Writing an example code
- Hubo basic example
from cs1robots import *
create_world()
hubo = Robot()
hubo.set_trace("blue")
hubo.move()
hubo.turn_left()
hubo.move()
hubo.turn_left()
hubo.move()
hubo.turn_left()
hubo.move()
hubo.turn_left()
15
THIS WEEK..
16
Tentative Schedule
Week1 Course Overview
Week16
-
Week2 Introduction to Python Programming
Week15
Final Exam
Week3 Python Programming Basics
Week14
Summary
Week4 Programming with Robots
Week13
Text Processing
Week5 Conditionals and If Statements
Week12
String, Set, Dictionary and Image Processing
Week6 While Loops vs For Loops
Week11
Sequences: Lists, Strings, and Tuples
Week7 Variables and Basic Data Types
Week10
Local/Global Variables
Week8 Midterm Exam
Week9
Functions with Parameters and Return Values
17
Table of contents
▪ Data Types
▪ Conditional Statements
▪ Loop Statements
▪ Functions
▪ Input & Output
▪ File Handling
18
Python Data Types
19
Python Data Types
▪
Python has the following data types built-in by default
-
▪
Text Type:
Numeric Types:
Sequence Types:
Mapping Type:
Set Types:
Boolean Type:
str
int, float, complex
list, tuple, range
dict
set, frozenset
bool
Getting the Data Type: type()
>>> x = 5
>>> print(type(x))
<class ‘int’>
20
Numbers
▪
Int
- Integer is a whole number, positive or negative, without decimals, of unlimited length
>>> a = 123
>>> a = -178
>>> a = 0
▪
Float
- Floating point number is a number, positive or negative, containing one or more decimals
>>> a = 1.2
>>> a = -3.45
- Float can also be scientific numbers with an "e" to indicate the power of 10
>>> a = 4.24E10
>>> a = 4.24e-10
21
Numbers – Arithmetic operators
▪
▪
The four fundamental arithmetic operators
- Addition, Subtraction, Multiplication, Division
>>> a = 3
>>> b = 4
>>> a + b # Addition
7
>>> a - b # Subtraction
-1
>>> a * b # Multiplication
12
>>> a / b # Division
0.75
The other operators
- Exponentiation
>>> a = 3
>>> b = 4
>>> a ** b
81
- Modulus
>>> 7 % 3
1
>>> 3 % 7
3
- Floor division
>>> 7 // 4
1
22
String
▪
Strings in python are surrounded by
- either single quotation marks, or double quotation mark
>>> print('Python')
Python
>>> print("Python")
Python
▪
Multiline Strings
- Using three single quotes, or three double quotes
>>> multiline='''
>>> multiline="""
... Life is too short
... Life is too short
... You need python
... You need python
... """
... '''
23
>>> print(multiline)
Life is too short
You need python
String
▪
Including single or double quotation marks in a string
- Single quotation mark
>>> food = "Python's favorite food is perl"
>>> food
"Python's favorite food is perl"
- Double quotation mark
>>> say = '"Python is very easy." he says.'
>>> say
"Python is very easy." he says
- Using backslash (\)
>>> food = 'Python\'s favorite food is perl'
>>> say = "\"Python is very easy.\" he says."
24
Lists
▪
Lists are used to store multiple items in a single variable
- Lists are created using square brackets [ ]
>>> odd = [1, 3, 5, 7, 9]
- List items can be of any data type
>>> a = [] # Empty list
>>> b = [1, 2, 3] # Number
>>> c = ['Life', 'is', 'too', 'short'] # String
>>> d = [1, 2, 'Life', 'is'] # Number + String
>>> e = [1, 2, ['Life', 'is']] # Number + List
25
Lists – Indexing
▪
List items are indexed
- The first item has index [0], the second item has index [1] etc.
>>>
>>>
[1,
>>>
1
>>>
4
>>>
3
>>> a = [1, 2, 3, ['a', 'b', 'c']]
>>> a[0] 1
>>> a[-1]
['a', 'b', 'c']
>>> a[3]
['a', 'b', 'c']
>>> a[-1][0]
'a'
>>> a[-1][1]
'b'
>>> a[-1][2]
'c'
a = [1, 2, 3]
a
2, 3]
a[0]
a[0] + a[2]
a[-1]
26
Lists – Change and Delete
▪
Change list items
- To change the value of a specific item, refer to the index number
>>> a = [1, 2, 3]
>>> a[2] = 4
>>> a [1, 2, 4]
▪
Delete list items
- Using del keyword to remove the specified index
>>> a = [1, 2, 3]
>>> del a[1]
>>> a
[1, 3]
27
Tuple
▪
A tuple is almost same as a list, but two things are different
- Tuples are written with round brackets ()
- Unchangeable: A tuple cannot change, add or remove their items
>>> t1 = ()
>>> t2 = (1,)
>>> t3 = (1, 2, 3)
>>> t4 = 1, 2, 3
>>> t5 = ('a', 'b', ('ab', 'cd'))
28
Tuple
▪
What if we try to delete or change an item in a tuple?
- When trying to delete an item in a tuple?
>>> t1 = (1, 2, 'a', 'b’)
>>> del t1[0]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object doesn't support item deletion
- When trying to change an item in a tuple?
>>> t1 = (1, 2, 'a', 'b’)
>>> t1[0] = 'c'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
29
Dictionary
▪
Dictionaries are used to store data values in “key:value” pairs
- Dictionaries are written with curly brackets { }, and have keys and values
- In key part, values are unchangeable,
but values can be both changeable and unchangeable in value part
>>> dic = {
key
value
'name':'pey',
name
pey
'phone':'0119993323’,
phone 01199993323
'birth': '1118’
}
birth
1118
>>> a = {1: 'hi'}
>>> a = {'a': [1,2,3]}
30
Dictionary
▪
Add a key:value pair in a dictionary
>>>
>>>
>>>
{1:
>>>
>>>
{1:
>>>
>>>
{1:
a = {1: 'a'}
a[2] = 'b' # add a 2:‘b’ pair in the dictionary a
a
'a', 2: 'b’}
a['name'] = 'pey' # add a ‘name’:‘pey’ pair in the dictionary a
a
'a', 2: 'b', 'name': 'pey’}
a[3] = [1,2,3] # add a 3:[1,2,3] pair in the dictionary a
a
'a', 2: 'b', 'name': 'pey', 3: [1, 2, 3]}
31
Dictionary
▪
Dictionary items can be referred to by using the key name
>>> grade = {'pey': 10, 'julliet': 99}
>>> grade['pey']
10
>>> grade['julliet']
99
>>> dic = {'name':'pey', 'phone':'0119993323', 'birth': '1118'}
>>> dic['name']
'pey'
>>> dic['phone']
'0119993323'
>>> dic['birth']
'1118'
32
Set
▪
Sets are the datatype for handling sets in mathematics
- Written with set keyword
>>> s1 = set([1,2,3])
>>> s1
{1, 2, 3}
- A set is a collection which is both unordered and unindexed.
Also, it does not allow duplicate (often used as a filter to remove duplicate data)
>>> s2 = set("Hello")
>>> s2
{'e', 'H', 'l', 'o'}
33
Set – mathematics
▪
▪
Union (U)
- Using ‘|’ and union method
>>> s1 | s2
{1, 2, 3, 4, 5, 6, 7, 8, 9}
>>> s1.union(s2)
{1, 2, 3, 4, 5, 6, 7, 8, 9}
Intersection (∩)
- Using ‘&’ and intersection method
>>> s1 = set([1, 2, 3, 4, 5, 6])
>>> s2 = set([4, 5, 6, 7, 8, 9])
>>> s1 & s2
{4, 5, 6}
>>> s1.intersection(s2)
{4, 5, 6}
▪
Difference (–)
- Using ‘–’ and difference method
>>> s1 - s2
{1, 2, 3}
>>> s2 - s1
{8, 9, 7}
>>> s1.difference(s2)
{1, 2, 3}
>>> s2.difference(s1)
{8, 9, 7}
34
Variables
▪
In Python, variables do not need to be declared with any particular data type
- If you create variable, just using assignment (=) symbol
>>> a = 1
>>> b = "python"
>>> c = [1,2,3]
▪
Python variables are pointers
>>> a = [1, 2, 3]
>>> id(a) # the address of the list [1, 2, 3]
4303029896
- A list data type (i.e., object) with a value of [1, 2, 3] is automatically created in the memory
- The variable a points the address of the memory where the list [1, 2, 3] is stored
35
Variable Names
▪
A variable can have a short name (e.g., x and y)
or a more descriptive name (age, carname, total_volume)
▪
Rules for Python variables
- Must start with a letter or the underscore character
- Cannot start with a number
- Can only contain alpha-numeric characters and underscores
- Case-sensitive
Legal variable name
Illegal variable names
myvar = "John"
my_var = "John"
_my_var = "John"
myVar = "John"
MYVAR = "John"
myvar2 = "John"
2myvar = "John"
my-var = "John"
my var = "John"
36
Variable Names
▪
There are several techniques you can use to make them more readable
- Camel case: Each word, except the first, starts with a capital letter
myVariableName = "John"
- Pascal case: Each word starts with a capital letter
MyVariableName = "John"
- Snake case: Each word is separated by an underscore character
my_variable_name = "John"
37
Conditional Statements
38
if Statement
▪
Basic structure
- An “if statement” is written by using if keyword
if condition:
statement 1
statement 2
...
>>> a = 33
>>> b = 200
>>> if b > a:
...
print("b is greater than a")
39
if Statement
▪
Basic structure
- It can also be used with else keyword
if condition:
>>>
statement 1
>>>
statement 2
>>>
...
...
else:
...
statement A
...
statement B
...
a = 33
b = 200
if b > a:
print("b is greater than a")
else:
print(“b is not greater than a")
40
Indentation
▪
All statements belonging to the if statement must be indented
- if statement without indentation will raise an error
- Indentation should always be the same width
money = True
money = True
if money:
if money:
print("Seo")
print("Seo")
print("Young")
print("Young")
print("Duk")
print("Duk")
41
money = True
if money:
print("Seo")
print("Young")
print("Duk")
Conditional Statement
▪
Conditional statement is a statement that judges true or false
- Using the comparison operators, the logical operators, and the membership operators
▪
Comparison operators
- Used to compare two values
>>> money = 2000
>>> if money >= 3000:
...
print("Take a taxi")
... else:
...
print("Just walk")
...
Just walk
Operator
Description
Example
<
Less than
x<y
>
Greater than
x>y
==
Equal
x == y
!=
Not equal
x != y
>=
Greater than or equal to
x >= y
<=
Less than or equal to
x <= y
42
Conditional Statement
▪
Logical operators
- Used to combine conditional statements
>>> money = 2000
>>> card = True
>>> if money >= 3000 or card:
...
print("Take a taxi")
... else:
Operator
...
print("Just walk")
...
and
Take a taxi
Description
Example
Return True if both
statements are true
x < 5 and x < 10
or
Returns True if one of the
statements is true
x < 5 or x < 4
not
Reverse the result, return
False if the result is True
not(x < 5 and x < 10)
43
Elif
▪
If the previous conditions were not true, then try this condition
- That is, elif is executed when
if condition:
statement 1
statement 2
...
elif condition:
statement 1
statement 2
...
else:
statement 1
statement 2
...
the previous conditional statement is false
>>> pocket = ['paper', 'cellphone’]
>>> card = True
>>> if 'money' in pocket:
...
print("Take a taxi")
... elif card:
...
print("Take a bus")
... else:
...
print("Just walk")
...
Take a bus
44
Loop Statements
45
Python Loops
▪
Python has two primitive loop commends
- while loops
>>> i = 1
>>> while i < 6:
...
print(i)
...
i += 1
- for loops
>>> fruits = ['apple', 'banana', 'cherry']
>>> for x in fruits:
...
print(x)
46
while loops
▪
Basic structure
- Can execute a set of statements as long as a condition is true
- The while loop requires relevant variables to be ready
while condition:
statement 1
statement 2
statement 3
...
47
while loops
▪
Example
- >>> treeHit = 0
>>> while treeHit < 10:
...
treeHit = treeHit +1
...
print("Cut down a tree, %d time." % treeHit)
...
if treeHit == 10:
...
print("A tree falls.")
...
treeHit
condition
statement
while statement
0
0 < 10
True
Cut down a tree, 1 time.
Loop
1
1 < 10
True
Cut down a tree, 2 time.
Loop
2
2 < 10
True
Cut down a tree, 3 time.
Loop
...
8
8 < 10
True
Cut down a tree, 9 time.
Loop
9
9 < 10
True
Cut down a tree, 10 time. A tree falls.
Loop
10
10 < 10
False
Complete
48
for loops
▪
Python for loops
- Used for iterating over a sequence that is either a list, a tuple, a dictionary, a set, or a string
- This is less like the for keyword in other programming languages
▪
Basic structure
- Can execute a set of statements, once for each item in a list, tuple, set etc.
for variable in list(or tuple, string):
statement 1
statement 2
...
49
for loops
▪
Example
- >>> test_list = ['one', 'two', 'three’]
>>> for i in test_list:
...
print(i)
...
one
two
three
- >>> for x in "banana":
...
print(x)
...
50
>>> a = [(1,2), (3,4), (5,6)]
>>> for (first, last) in a:
...
print(first + last)
...
3
7
11
for loops
▪
Advanced example
- A total of 5 students took a test. If the test score is over 60, it’s a pass. Otherwise, it’s a fail.
Show the results of a pass or fail of each student.
- marks = [90, 25, 67, 45, 80]
Student
Student
Student
Student
Student
1
2
3
4
5
passed
failed
passed
failed
passed
number = 0
for mark in marks:
number = number +1
if mark >= 60:
print("Student %d passed the test." % number)
else:
print("Student %d failed the test." % number)
51
the
the
the
the
the
test.
test.
test.
test.
test.
range() function
▪
The range() function returns a sequence of numbers
- Starting from 0 by default, and increments by 1 (by default), and ends at a specified number
>>> a = range(10)
>>> a
range(0, 10) # a range object containing numbers from 0 to less than 10
- To specify the starting value by adding a parameter
>>> a = range(1, 11)
>>> a
range(1, 11) # a range object containing numbers from 1 to less than 11
- To specify the increment value by adding a third parameter
>>> a = range(2, 30, 3)
>>> a
range(2, 30, 3) # a range object containing numbers from 2 to less than 30
and increments by 3
52
range() function
▪
To loop through a set of code a specified number of times for a Python for loop
- Mainly using range() function
>>> for x in range(6):
...
print(x)
>>> add = 0
>>> for i in range(1, 11):
...
add = add + i
...
>>> print(add)
>>> for x in range(2, 6):
...
print(x)
>>> for x in range(2, 30, 3):
...
print(x)
53
Functions
54
Python Functions
▪
What is the functions?
- A function is a block of code which only runs when it is called
- You can pass data, known as parameters, into a function
- A function can return data as a result
▪
Why we use the functions?
- If you anticipate needing to repeat the same or very similar code more than once,
it may be worth writing a reusable function
- Can also help make your code more readable
55
Python Functions
▪
Basic Structure
- In Python, a function is defined using the def keyword
def name(parameters):
statement1
statement2
...
- Example
>>> def add(a, b):
...
return a+b
...
>>>
>>>
>>>
>>>
>>>
7
a = 3
b = 4
c = add(a, b)
print(c)
56
Parameters & Arguments
▪
What is the difference between a parameter and an argument
- A parameter – the variable listed inside the parentheses in the function definition
- An argument – the value that is sent to the function when it is called
def add(a, b): # a and b are parameters
return a+b
print(add(3, 4)) # 3 and 4 are arguments
57
Types of Functions in Python
▪
There are 4 types of function in Python
-
▪
A function with argument and return value
With no argument and with a return value
With argument and no return value
With no argument and no return value
A function with argument and return value
>>> def add(a, b):
...
result = a + b
...
return result
...
>>> a = add(3, 4)
>>> print(a)
7
- def name(parameters):
statement
...
return result
58
Types of Functions in Python
▪
A function with no argument and with a return value
- def name():
statement
...
return result
▪
>>> def say():
...
return 'Hi’
...
>>> a = say()
>>> print(a)
Hi
A function with argument and no return value
- def name(paramenter):
statement
...
>>> a = add(3, 4)
3, 4의 합은 7입니다.
>>> a = add(3, 4)
>>> print(a)
None
>>> def add(a, b):
...
print("%d, %d의 합은 %d입니다." % (a, b, a+b))
...
>>> add(3, 4)
3, 4의 합은 7입니다.
59
Types of Functions in Python
▪
A function with no argument and no return value
- def name():
statement
...
>>> def say():
...
print('Hi’)
...
>>> say()
Hi
60
Return values
▪
What if we call this function?
>>>
...
...
>>>
>>>
>>>
>>>
▪
def add_and_mul(a,b):
return a+b, a*b
result = add_and_mul(3,4)
result1, result2 = add_and_mul(3, 4)
print(result)
print(result1, result2)
A function always has one return value
How about this function?
- >>> def add_and_mul(a,b):
...
return a+b
...
return a*b
...
>>> result = add_and_mul(2, 3)
>>> print(result)
5
61
Input & Output
62
User Input
▪
Python uses the input() method and gets input from the users
- An input() method treats every input as a string
>>> a = input()
Life is too short, you need python
>>> a
'Life is too short, you need python'
- The prompt argument is used to display a message to the user (optional)
>>> number = input("Please enter a number: ")
Please enter a number: 3
>>> print(number)
3
>>> type(number)
<class 'str'>
63
Print
▪
The print() function prints the specified message
- Can take any number of arguments, but can only have one expression
▪
Basic structure
- Print(object(s), sep=separator, end=end, file=file, flush=flush)
Parameter
Description
object(s)
Any object, and as many as you like. Will be converted to string before printed
sep=separator
Optional. Specify how to separate the objects, if there is more than one. Default is ' '
end=end
Optional. Specify what to print at the end. Default is '\n' (line feed)
64
Print
▪
Using a sep parameter
- Default is ' '
>>> print("life", "is", "too short")
life is too short
- Specify the separator
>>> print("010", "111", "1234", sep="-")
010-111-1234
▪
Using an end parameter
- Default is '\n'
>>> for i in range(3):
...
print(i)
...
0
1
2
- Specify the end
>>> for i in range(10):
...
print(i, end=' ')
...
0 1 2 3 4 5 6 7 8 9
65
File Handling
66
File open
▪
The key function for working with files in Python is the open() function
- The open() function takes two parameters; filename, and mode
f = open(filename, mode) # f is file object
- A file is located in the same directory as a Python file
f = open("new_file.txt", "r")
f.close()
Mode
f = open("new_file.txt", "w")
f.close()
r
- If the file is located in a different location,
you will have to specify the file path
f = open("C:/opensourse/new_file.txt")
f.close()
67
Description
Read (Default value) – Opens a file for
reading, error if the file does not exist
w
Write – Open a file for writing, create
the file if it does not exist
a
Append – Open a file for appending,
creates the file if it does not exist
Write Files
▪
Create a new file
- Using the open() method with write mode (w)
# writedata.py
f = open("C:/opensourse/newfile.txt", 'w')
for i in range(1, 11):
data = "This is line %d.\n" % i
f.write(data)
f.close()
68
Read Files
▪
There are several ways to read a file
This is line 1.
- Using readline() function
# readline_test.py
f = open("C:/opensourse/newfile.txt", 'r')
line = f.readline()
print(line)
f.close()
- If you want to read all lines
# readline_all.py
f = open("C:/opensourse/newfile.txt", 'r')
while True:
line = f.readline()
if not line: break
print(line)
f.close()
69
This
This
This
This
This
This
This
This
This
This
is
is
is
is
is
is
is
is
is
is
line
line
line
line
line
line
line
line
line
line
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Read Files
▪
There are several ways to read a file
- Using readlines() function
# readlines_test.py
f = open("C:/opensourse/newfile.txt", 'r')
lines = f.readlines() # list
for line in lines:
print(line)
f.close()
- Using read() function – return a string
# read_test.py
f = open("C:/opensourse/newfile.txt", 'r')
data = f.read() # string
print(data)
f.close()
70
This
This
This
This
This
This
This
This
This
This
is
is
is
is
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Append Data in a File
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Write to an existing file
- Using write mode (w) – will overwrite any existing content
- Using append mode (a) – will append to the end of the file
# adddata.py
f = open("C:/opensourse/newfile.txt", 'a')
for i in range(11, 21):
data = "This is line %d.\n" % i
f.write(data)
f.close()
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Summary
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Lecture Summary
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Python Programming Basic
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Data types (Number, String, List, Tuple, Dictionary, Set)
Conditional statements (if statement)
Loop statements (while & for statements)
Functions (parameter, argument, return value)
Input & Output (input method, print function)
File Handling (file open, write file, read file, append data in a file)
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We will learn the chapter 4.
Programming with
Robots
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Thanks for listening
Knowledge-based Data Discovery
INHA KDD Lab.