Python Tutorial

Every time a user submits an input, it must be validated to see if it is exactly what we expected. We can validate the input in one of two ways: by applying a flag variable or implementing try or except. The flag variable will be originally set to false, and if we determine that the given data is the same as our expectation, we will change the flag status to true. From there, we can determine what we can do next, depending on the flag status. If the result is unfavorable, the except code block is executed.

Types of Validation in Python

Broadly we can categorize the validation problems into these three categories:

Type Check: The supplied data type is verified using one of the Python validation methods. The Python data types are such as int, float, etc.

Length Check: The length of the provided input string or any iterable is verified using any of the described Python validation methods.

Range Check: Python's validation method can also be implemented to determine whether the supplied input number falls between the two specified numbers.

Below we have described the Syntax of validation methods:

Syntax using the flag:

# Syntax of using the flag variable to validate an input

flag = False
while not flag:
     if [put condition here]:
            flag = True
     else:
          print('Input is not Valid')

The flag's status is originally set to false, and the exact condition is considered during a while loop to keep the statement from becoming true. If the required validation condition is fulfilled, the flag is validated and set to true; if not, an error message is produced.

# Syntax of using the try-except code block to validate an input

# Starting a while loop to always run this code
while True:
        # Starting a try block
        try:
            [Here, put the code which may contain an error]
       except:
           
print('This error message will be displayed if the code will have any error')

print('If the code written in the try block of the code above runs successfully, execute the code further from this point.')

We first set the condition of the while loop to be true and, after that, run a code block to perform the required validation. If the code cannot complete the verification, an exception will be raised that displays the error message. A success text is printed if the try code block successfully completes the code.

Examples of Python Validation

Examples show the implementation of the validation methods described above.

Example- 1

We will check whether the input has the required data type.

Code

# Python program to show how to use the flag variable to check the data type of the input variable

# Declaring a variable valid, which will work as a flag variable and will set it to False
valid = False

# Giving the flag variable as the condition of the while loop
# If the condition is true, it will prompt us to enter the input
while not valid:
    #The user will be prompted to give the input
    number = input('Please type a number: ')
    # We will check the input given by the user to see if it is of int data type
    if number.isdigit():
        #The flag variable is set to true if the condition in this if statement is true
        valid = True
    else:
        print('The input given is not a valid integer')
        # This will print this output if the input given by the user is of integer data type
    print('The given input is an integer and that is: ' + str(number))

Output

Please type a number: 8.8
The input given is not a valid integer
The given input is an integer and that is: 8.8

Example- 2

The Python program validates the user-provided input using a flag variable to see if it falls inside a certain range.

Code

# Python program to show how to use the flag variable to check the range of the input variable lies in the specified range

# Declaring a variable valid, which will work as a flag variable and will set it to False
valid = False

# Giving the flag variable as the condition of the while loop
# If the condition is true, it will prompt us to enter the input
while not valid:
    # The user will be prompted to give the input
    number = int(input('Please type a number: '))
    # We will check the input given by the user to see if it lies in the specified range
    if number >= 13 and number <= 19:
        valid = True
    else:
      print('The number given by you does not lie between 13 and 19')
    # This output will be printed if the input given by the user lies between the specified range
    print('The number given by the user lies between 13 and 19 and the number given by you is: ' + str(number))

Output

Please type a number: 7
The number given by you does not lie between 13 and 19
The number given by the user lies between 13 and 19 and the number given by you is: 7

Example- 3

The Python program uses the flag variable to determine the input of the string's length.

Code

# Python program to show how to use the flag variable to check the range of the input variable

# Declaring a variable valid, which will work as a flag variable and will set it to False
valid = False

# Giving the flag variable as the condition of the while loop
# If the condition is true, it will prompt us to enter the input
while not valid:
    #The user will be prompted to give the input
    string = input('Please give a string: ')
    # We will check the input given by the user to see if it has a length greater than or equal to 5
    if len(string) >= 5:
        #The flag variable is set to true if the condition in this if statement is true
        valid = True
    else:
        print('The input string given has length less than 5')
        #This output will be printed if the input string given by the user has a specified length
    print('The given input string has a length greater than or equal to 5, and the string is: ' + string)

Output

Please give a string: Python
The given input string has a length greater than or equal to 5, and the string is: Python

Benefits

It aids in enhancing code security.
Python's validation feature stops outside users from mistakenly or purposefully misusing the code.
We may use it to determine whether or not the given data type is valid.
We may use it to determine whether the input provided has any incorrect values.
We can use it to determine whether an input falls within or outside the range.
We may use it to determine whether the provided input complies with the limits placed on it.
We may use it to determine whether or not the input is consistent.
We may use Python's validation feature to determine whether an input is legitimate.
We may use Python's validation feature to determine whether the provided input variable is complete.