Python For Beginners (தமிழ்)

Variables

Variables are containers for storing data values.

Creating Variables

Python has no command for declaring a variable.

A variable is created the moment you first assign a value to it.

Example

x = 5
y = "John"
print(x)
print(y)

Built-in Data Types

In programming, data type is an important concept.

Variables can store data of different types, and different types can do different things.

Python has the following data types built-in by default, in these categories:

Text Type:str

Numeric Types:int, float, complex

Sequence Types:list, tuple, range

Mapping Type:dict

Set Types:set, frozenset

Boolean Type:bool

Binary Types:bytes, bytearray, memoryview

Getting the Data Type

You can get the data type of any object by using the type() function:

Example

Print the data type of the variable x:

x = 5
print(type(x))

Python Numbers

There are three numeric types in Python:

• int

• float

• complex

Variables of numeric types are created when you assign a value to them:

Example

x = 1 # int
y = 2.8 # float
z = 1j # complex

print(type(x))

print(type(y))

print(type(z))

Casting :

Specify a Variable Type

There may be times when you want to specify a type on to a variable. This can be done with casting. Python is an object-orientated language, and as such it uses classes to define data types, including its primitive types.

Casting in python is therefore done using constructor functions:

• int() - constructs an integer number from an integer literal, a float literal (by rounding down to the previous whole number), or a string literal (providing the string represents a whole number)

• float() - constructs a float number from an integer literal, a float literal or a string literal (providing the string represents a float or an integer)

• str() - constructs a string from a wide variety of data types, including strings, integer literals and float literals

Example

Integers:

x = int(1) # x will be 1
y = int(2.8) # y will be 2
z = int("3") # z will be 3

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Example

Floats:

x = float(1) # x will be 1.0
y = float(2.8) # y will be 2.8
z = float("3") # z will be 3.0
w = float("4.2") # w will be 4.2

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Example

Strings:

x = str("s1") # x will be 's1'
y = str(2) # y will be '2'
z = str(3.0) # z will be '3.0'

Strings

Strings in python are surrounded by either single quotation marks, or double quotation marks.

'hello' is the same as "hello".

You can display a string literal with the print() function:

Example

print("Hello")
print('Hello')

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Assign String to a Variable

Assigning a string to a variable is done with the variable name followed by an equal sign and the string:

Example

a = "Hello"
print(a)

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Multiline Strings

You can assign a multiline string to a variable by using three quotes:

Example

You can use three double quotes:

a = """Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua."""
print(a)

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Or three single quotes:

Example

a = '''Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua.'''
print(a)

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Note: in the result, the line breaks are inserted at the same position as in the code.

Strings are Arrays

Like many other popular programming languages, strings in Python are arrays of bytes representing unicode characters.

However, Python does not have a character data type, a single character is simply a string with a length of 1.

Square brackets can be used to access elements of the string.

Example

Get the character at position 1 (remember that the first character has the position 0):

a = "Hello, World!"
print(a[1])

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Looping Through a String

Since strings are arrays, we can loop through the characters in a string, with a for loop.

Example

Loop through the letters in the word "banana":

for x in "banana":
print(x)

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Learn more about For Loops in our Python For Loops chapter.

String Length

To get the length of a string, use the len() function.

Example

The len() function returns the length of a string:

a = "Hello, World!"
print(len(a))

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Check String

To check if a certain phrase or character is present in a string, we can use the keyword in.

Example

Check if "free" is present in the following text:

txt = "The best things in life are free!"
print("free" in txt)

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Use it in an if statement:

Example

Print only if "free" is present:

txt = "The best things in life are free!"
if "free" in txt:
print("Yes, 'free' is present.")

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Learn more about If statements in our Python If...Else chapter.

Check if NOT

To check if a certain phrase or character is NOT present in a string, we can use the keyword not in.

Example

Check if "expensive" is NOT present in the following text:

txt = "The best things in life are free!"
print("expensive" not in txt)

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Use it in an if statement:

Example

print only if "expensive" is NOT present:

txt = "The best things in life are free!"
if "expensive" not in txt:
print("Yes, 'expensive' is NOT present.")

Booleans represent one of two values: True or False.

Boolean Values

In programming you often need to know if an expression is True or False.

You can evaluate any expression in Python, and get one of two answers, True or False.

When you compare two values, the expression is evaluated and Python returns the Boolean answer:

Example

print(10 > 9)
print(10 == 9)
print(10 < 9)

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When you run a condition in an if statement, Python returns True or False:

Example

Print a message based on whether the condition is True or False:

a = 200
b = 33

if b > a:
print("b is greater than a")
else:
print("b is not greater than a")

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Evaluate Values and Variables

The bool() function allows you to evaluate any value, and give you True or False in return,

Example

Evaluate a string and a number:

print(bool("Hello"))
print(bool(15))

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Example

Evaluate two variables:

x = "Hello"
y = 15

print(bool(x))
print(bool(y))

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Most Values are True

Almost any value is evaluated to True if it has some sort of content.

Any string is True, except empty strings.

Any number is True, except 0.

Any list, tuple, set, and dictionary are True, except empty ones.

Example

The following will return True:

bool("abc")
bool(123)
bool(["apple", "cherry", "banana"])

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Some Values are False

In fact, there are not many values that evaluate to False, except empty values, such as (), [], {}, "", the number 0, and the value None. And of course the value False evaluates to False.

Example

The following will return False:

bool(False)
bool(None)
bool(0)
bool("")
bool(())
bool([])
bool({})

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One more value, or object in this case, evaluates to False, and that is if you have an object that is made from a class with a __len__ function that returns 0 or False:

Example

class myclass():
def __len__(self):
return 0

myobj = myclass()
print(bool(myobj))

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Functions can Return a Boolean

You can create functions that returns a Boolean Value:

Example

Print the answer of a function:

def myFunction() :
return True

print(myFunction())

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You can execute code based on the Boolean answer of a function:

Example

Print "YES!" if the function returns True, otherwise print "NO!":

def myFunction() :
return True

if myFunction():
print("YES!")
else:
print("NO!")

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Python also has many built-in functions that return a boolean value, like the isinstance() function, which can be used to determine if an object is of a certain data type:

Example

Check if an object is an integer or not:

x = 200
print(isinstance(x, int))

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Test Yourself With Exercises

Exercise:

The statement below would print a Boolean value, which one?

print(10 > 9)

mylist = ["apple", "banana", "cherry"]

List

Lists are used to store multiple items in a single variable.

Lists are one of 4 built-in data types in Python used to store collections of data, the other 3 are Tuple, Set, and Dictionary, all with different qualities and usage.

Lists are created using square brackets:

Example

Create a List:

thislist = ["apple", "banana", "cherry"]
print(thislist)

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List Items

List items are ordered, changeable, and allow duplicate values.

List items are indexed, the first item has index [0], the second item has index [1] etc.

Ordered

When we say that lists are ordered, it means that the items have a defined order, and that order will not change.

If you add new items to a list, the new items will be placed at the end of the list.

Note: There are some list methods that will change the order, but in general: the order of the items will not change.

Changeable

The list is changeable, meaning that we can change, add, and remove items in a list after it has been created.

Allow Duplicates

Since lists are indexed, lists can have items with the same value:

Example

Lists allow duplicate values:

thislist = ["apple", "banana", "cherry", "apple", "cherry"]
print(thislist)

List Length

To determine how many items a list has, use the len() function:

Example

Print the number of items in the list:

thislist = ["apple", "banana", "cherry"]
print(len(thislist))

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List Items - Data Types

List items can be of any data type:

Example

String, int and boolean data types:

list1 = ["apple", "banana", "cherry"]
list2 = [1, 5, 7, 9, 3]
list3 = [True, False, False]

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A list can contain different data types:

Example

A list with strings, integers and boolean values:

list1 = ["abc", 34, True, 40, "male"]

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type()

From Python's perspective, lists are defined as objects with the data type 'list':

<class 'list'>

Example

What is the data type of a list?

mylist = ["apple", "banana", "cherry"]
print(type(mylist))

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The list() Constructor

It is also possible to use the list() constructor when creating a new list.

Example

Using the list() constructor to make a List:

thislist = list(("apple", "banana", "cherry")) # note the double round-brackets
print(thislist)

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Python Collections (Arrays)

There are four collection data types in the Python programming language:

• List is a collection which is ordered and changeable. Allows duplicate members.

• Tuple is a collection which is ordered and unchangeable. Allows duplicate members.

• Set is a collection which is unordered and unindexed. No duplicate members.

• Dictionary is a collection which is unordered and changeable. No duplicate members.

When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.

mytuple = ("apple", "banana", "cherry")

Tuple

Tuples are used to store multiple items in a single variable.

Tuple is one of 4 built-in data types in Python used to store collections of data, the other 3 are List, Set, and Dictionary, all with different qualities and usage.

A tuple is a collection which is ordered and unchangeable.

Tuples are written with round brackets.

Example

Create a Tuple:

thistuple = ("apple", "banana", "cherry")
print(thistuple)

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Tuple Items

Tuple items are ordered, unchangeable, and allow duplicate values.

Tuple items are indexed, the first item has index [0], the second item has index [1] etc.

Ordered

When we say that tuples are ordered, it means that the items have a defined order, and that order will not change.

Unchangeable

Tuples are unchangeable, meaning that we cannot change, add or remove items after the tuple has been created.

Allow Duplicates

Since tuple are indexed, tuples can have items with the same value:

Example

Tuples allow duplicate values:

thistuple = ("apple", "banana", "cherry", "apple", "cherry")
print(thistuple)

myset = {"apple", "banana", "cherry"}

Set

Sets are used to store multiple items in a single variable.

Set is one of 4 built-in data types in Python used to store collections of data, the other 3 are List, Tuple, and Dictionary, all with different qualities and usage.

A set is a collection which is both unordered and unindexed.

Sets are written with curly brackets.

Example

Create a Set:

thisset = {"apple", "banana", "cherry"}
print(thisset)

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Note: Sets are unordered, so you cannot be sure in which order the items will appear.

Set Items

Set items are unordered, unchangeable, and do not allow duplicate values.

Unordered

Unordered means that the items in a set do not have a defined order.

Set items can appear in a different order every time you use them, and cannot be referred to by index or key.

Unchangeable

Sets are unchangeable, meaning that we cannot change the items after the set has been created.

Once a set is created, you cannot change its items, but you can add new items.

Duplicates Not Allowed

Sets cannot have two items with the same value.

Example

Duplicate values will be ignored:

thisset = {"apple", "banana", "cherry", "apple"}

print(thisset)

Get the Length of a Set

To determine how many items a set has, use the len() method.

Example

Get the number of items in a set:

thisset = {"apple", "banana", "cherry"}

print(len(thisset))

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Set Items - Data Types

Set items can be of any data type:

Example

String, int and boolean data types:

set1 = {"apple", "banana", "cherry"}
set2 = {1, 5, 7, 9, 3}
set3 = {True, False, False}

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A set can contain different data types:

Example

A set with strings, integers and boolean values:

set1 = {"abc", 34, True, 40, "male"}

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type()

From Python's perspective, sets are defined as objects with the data type 'set':

<class 'set'>

Example

What is the data type of a set?

myset = {"apple", "banana", "cherry"}
print(type(myset))

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The set() Constructor

It is also possible to use the set() constructor to make a set.

Example

Using the set() constructor to make a set:

thisset = set(("apple", "banana", "cherry")) # note the double round-brackets
print(thisset)

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Python Collections (Arrays)

There are four collection data types in the Python programming language:

• List is a collection which is ordered and changeable. Allows duplicate members.

• Tuple is a collection which is ordered and unchangeable. Allows duplicate members.

• Set is a collection which is unordered and unindexed. No duplicate members.

• Dictionary is a collection which is unordered and changeable. No duplicate members.

When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}

Dictionary

Dictionaries are used to store data values in key:value pairs.

A dictionary is a collection which is unordered, changeable and does not allow duplicates.

Dictionaries are written with curly brackets, and have keys and values:

Example

Create and print a dictionary:

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(thisdict)

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Dictionary Items

Dictionary items are unordered, changeable, and does not allow duplicates.

Dictionary items are presented in key:value pairs, and can be referred to by using the key name.

Example

Print the "brand" value of the dictionary:

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(thisdict["brand"])

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Unordered

When we say that dictionaries are unordered, it means that the items does not have a defined order, you cannot refer to an item by using an index.

Changeable

Dictionaries are changeable, meaning that we can change, add or remove items after the dictionary has been created.

Duplicates Not Allowed

Dictionaries cannot have two items with the same key:

Example

Duplicate values will overwrite existing values:

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964,
"year": 2020
}
print(thisdict)

Dictionary Length

To determine how many items a dictionary has, use the len() function:

Example

Print the number of items in the dictionary:

print(len(thisdict))

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Dictionary Items - Data Types

The values in dictionary items can be of any data type:

Example

String, int, boolean, and list data types:

thisdict = {
"brand": "Ford",
"electric": False,
"year": 1964,
"colors": ["red", "white", "blue"]
}

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type()

From Python's perspective, dictionaries are defined as objects with the data type 'dict':

<class 'dict'>

Example

Print the data type of a dictionary:

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(type(thisdict))

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Python Collections (Arrays)

There are four collection data types in the Python programming language:

• List is a collection which is ordered and changeable. Allows duplicate members.

• Tuple is a collection which is ordered and unchangeable. Allows duplicate members.

• Set is a collection which is unordered and unindexed. No duplicate members.

• Dictionary is a collection which is unordered and changeable. No duplicate members.

When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.

Python Conditions and If statements

Python supports the usual logical conditions from mathematics:

• Equals: a == b

• Not Equals: a != b

• Less than: a < b

• Less than or equal to: a <= b

• Greater than: a > b

• Greater than or equal to: a >= b

These conditions can be used in several ways, most commonly in "if statements" and loops.

An "if statement" is written by using the if keyword.

Example

If statement:

a = 33
b = 200
if b > a:
print("b is greater than a")

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In this example we use two variables, a and b, which are used as part of the if statement to test whether b is greater than a. As a is 33, and b is 200, we know that 200 is greater than 33, and so we print to screen that "b is greater than a".

Indentation

Python relies on indentation (whitespace at the beginning of a line) to define scope in the code. Other programming languages often use curly-brackets for this purpose.

Example

If statement, without indentation (will raise an error):

a = 33
b = 200
if b > a:
print("b is greater than a") # you will get an error

Elif

The elif keyword is pythons way of saying "if the previous conditions were not true, then try this condition".

Example

a = 33
b = 33
if b > a:
print("b is greater than a")
elif a == b:
print("a and b are equal")

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In this example a is equal to b, so the first condition is not true, but the elif condition is true, so we print to screen that "a and b are equal".

Else

The else keyword catches anything which isn't caught by the preceding conditions.

Example

a = 200
b = 33
if b > a:
print("b is greater than a")
elif a == b:
print("a and b are equal")
else:
print("a is greater than b")

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In this example a is greater than b, so the first condition is not true, also the elif condition is not true, so we go to the else condition and print to screen that "a is greater than b".

You can also have an else without the elif:

Example

a = 200
b = 33
if b > a:
print("b is greater than a")
else:
print("b is not greater than a")

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Short Hand If

If you have only one statement to execute, you can put it on the same line as the if statement.

Example

One line if statement:

if a > b: print("a is greater than b")

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Short Hand If ... Else

If you have only one statement to execute, one for if, and one for else, you can put it all on the same line:

Example

One line if else statement:

a = 2
b = 330
print("A") if a > b else print("B")

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This technique is known as Ternary Operators, or Conditional Expressions.

You can also have multiple else statements on the same line:

Example

One line if else statement, with 3 conditions:

a = 330
b = 330
print("A") if a > b else print("=") if a == b else print("B")

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And

The and keyword is a logical operator, and is used to combine conditional statements:

Example

Test if a is greater than b, AND if c is greater than a:

a = 200
b = 33
c = 500
if a > b and c > a:
print("Both conditions are True")

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Or

The or keyword is a logical operator, and is used to combine conditional statements:

Example

Test if a is greater than b, OR if a is greater than c:

a = 200
b = 33
c = 500
if a > b or a > c:
print("At least one of the conditions is True")

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Nested If

You can have if statements inside if statements, this is called nested if statements.

Example

x = 41

if x > 10:
print("Above ten,")
if x > 20:
print("and also above 20!")
else:
print("but not above 20.")

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The pass Statement

if statements cannot be empty, but if you for some reason have an if statement with no content, put in the pass statement to avoid getting an error.

Example

a = 33
b = 200

if b > a:
pass