learnpython24-(Data types and Type casting)

 

Data Types in Python

Primarily there are following data types in Python.

1. Integers (<class 'int'>): Used to store integers
2. Floating point numbers (<class 'float'>): Used to store decimal or floating-point numbers
3. Strings (<class 'str'>): Used to store strings
4. Booleans (<class 'bool'>): Used to store True/False type values
5. None: None is a literal to describe 'Nothing' in Python 

Rules for defining a variable in Python:

• A variable name can contain alphabets, digits, and underscores (_). For E.g. : demo_xyz = ‘It’s a string variable’
• A variable name can only start with an alphabet and underscore.
• It can't start with a digit. 5aman is illegal and not allowed
• No white-space is allowed to be used inside a variable name.
• Also, reserved keywords are not recommended to be used as variable names.

Examples of few valid variable names are aman, _demo, de_mo, etc.

Python is a fantastic language that automatically identifies the type of data for us. It means we need to put some data in a variable, and Python automatically understands the kind of data a variable is holding. Cool, isn't it?

Have a look at the code below:

 

type() Function in Python: type() function is a function that allows a user to find data type of any variable. It returns the data type of any data contained in the variable passed to it.
Have a look at the code below which depicts the use of type function:

Note – We can't do arithmetic operations of numbers with strings i.e. we can't add a string to any number. Have a look at the example below:

Note – We can add (concatenate) two or more strings and the strings will be concatenated to return another string. Heres the example showing that:

Typecasting :

Typecasting is a way to change the data type of one data to another i.e. it changes the data type of any variable to some other data type.

I know it's a bit confusing but let me tell you in a simple manner. Suppose there is a string "34" (note string not integer since it is enclosed in double-quotes) and as we know we can't add this to an integer number let's say 6. But to do so we can typecast this string to int data type and then we can add 34+6 to get the output as 40. Have a look at the program below.

There are many functions to convert one data type into another type :

str() – this function allows us to convert some other data type into a string.

int() – this function allows us to convert some other data type into an integer. For example, str("34") returns 34 which is of type integer (int)

float() – this function allows us to convert some other data type into floating-point number i.e. a number with decimals.

input() Function – This function allows the user to receive input from the keyboard into the program as a string. 
input() function always takes input as a string i.e. if we ask the user to input a number even then it will take it as a string and we will have to typecast it into another data type as per the use case.
If you enter 45 when input() is called, you will get "45" as a string

Quick Quiz: Create a program that takes two numbers as input from the user and then prints the sum of these numbers.

Solution : :

Python Type Conversion and Type Casting

In this article, you will learn about the Type conversion and uses of type conversion.

Before learning Type Conversion in Python, you should have knowledge about python data types.

Type Conversion

The process of converting the value of one data type (integer, string, float, etc.) to another data type is called type conversion. Python has two types of type conversion.

1. Implicit Type Conversion
2. Explicit Type Conversion

Implicit Type Conversion

In Implicit type conversion, Python automatically converts one data type to another data type. This process doesn't need any user involvement.

Let's see an example where Python promotes the conversion of the lower data type (integer) to the higher data type (float) to avoid data loss.

Example 1: Converting integer to float

num_int = 123
num_flo = 1.23

num_new = num_int + num_flo

print("datatype of num_int:",type(num_int))
print("datatype of num_flo:",type(num_flo))

print("Value of num_new:",num_new)
print("datatype of num_new:",type(num_new))

When we run the above program, the output will be:

datatype of num_int: <class 'int'>
datatype of num_flo: <class 'float'>

Value of num_new: 124.23
datatype of num_new: <class 'float'>

In the above program,

• We add two variables num_int and num_flo, storing the value in num_new.
• We will look at the data type of all three objects respectively.
• In the output, we can see the data type of num_int is an integer while the data type of num_flo is a float.
• Also, we can see the num_new has a float data type because Python always converts smaller data types to larger data types to avoid the loss of data.

Now, let's try adding a string and an integer, and see how Python deals with it.

Example 2: Addition of string(higher) data type and integer(lower) datatype

num_int = 123
num_str = "456"

print("Data type of num_int:",type(num_int))
print("Data type of num_str:",type(num_str))

print(num_int+num_str)

When we run the above program, the output will be:

Data type of num_int: <class 'int'> 
Data type of num_str: <class 'str'> 

Traceback (most recent call last): 
  File "python", line 7, in <module> 
TypeError: unsupported operand type(s) for +: 'int' and 'str'

In the above program,

• We add two variables num_int and num_str.
• As we can see from the output, we got TypeError. Python is not able to use Implicit Conversion in such conditions.
• However, Python has a solution for these types of situations which is known as Explicit Conversion.

Explicit Type Conversion

In Explicit Type Conversion, users convert the data type of an object to required data type. We use the predefined functions like int(), float(), str(), etc to perform explicit type conversion.

This type of conversion is also called typecasting because the user casts (changes) the data type of the objects.

Syntax :

<required_datatype>(expression)

Typecasting can be done by assigning the required data type function to the expression.

Example 3: Addition of string and integer using explicit conversion

num_int = 123
num_str = "456"

print("Data type of num_int:",type(num_int))
print("Data type of num_str before Type Casting:",type(num_str))

num_str = int(num_str)
print("Data type of num_str after Type Casting:",type(num_str))

num_sum = num_int + num_str

print("Sum of num_int and num_str:",num_sum)
print("Data type of the sum:",type(num_sum))

When we run the above program, the output will be:

Data type of num_int: <class 'int'>
Data type of num_str before Type Casting: <class 'str'>

Data type of num_str after Type Casting: <class 'int'>

Sum of num_int and num_str: 579
Data type of the sum: <class 'int'>

In the above program,

• We add num_str and num_int variable.
• We converted num_str from string(higher) to integer(lower) type using int() function to perform the addition.
• After converting num_str to an integer value, Python is able to add these two variables.
• We got the num_sum value and data type to be an integer.

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Key Points to Remember

1. Type Conversion is the conversion of object from one data type to another data type.
2. Implicit Type Conversion is automatically performed by the Python interpreter.
3. Python avoids the loss of data in Implicit Type Conversion.
4. Explicit Type Conversion is also called Type Casting, the data types of objects are converted using predefined functions by the user.
5. In Type Casting, loss of data may occur as we enforce the object to a specific data type.

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