# Check if input is integer in Python

There is wide use of input statements in the programming world. In Python, we use the `input()` function to take in the input from the user. The data entered could be of any data type provided by Python. Sometimes the data type of the input needs to be checked and specified.

This article focuses on how to check if input is integer in Python.

## Using the `isdigit()` method to check if input is integer in Python.

The `isdigit()` function, when implemented on the input, returns `True` if the input of the string is a number containing only the digits `0-9`.

However, we should note that this method fails to deliver when the input is a negative number.

The following code uses the `isdigit()` method to check if input is integer in Python.

The above code provides the following output:

Enter the input : 7
True

Let’s run the sample program for negative number.

Enter the input : -20
False

As you can see, it returned false for negative number.

## Using the `isnumeric()` method to check if input is integer in Python.

The `isnumeric()` function runs similar to the `isdigit()` function mentioned in the article above. It provides a `True` value if the encountered input contains solely the digits `0-9`.

Like the `isdigit()` function, this function is unusable when the input contains any negative values as it automatically displays the `False` value when a `-` sign is encountered. Decimals with the dot `.` sign is also not considered to be numeric values in the `isnumeric()` function.

The following code uses the `isnumeric()` method to check if input is integer in Python.

The above code provides the following output:

Enter the input : 7
True

Let’s run the sample program for negative number.

Enter the input : -100
False

As you can see, `isnumeric()` also returned false for negative number.

Both the `isdigit()` and `isnumeric()` functions have similar working and functioning. However, the `isnumeric()` function differs from the `isdigit()` function is due to the fact that the `isnumeric()` function returns a `True` value even if it encounters any numbers in other languages. This is not the case with the `isdigit()` function, which displays `False`.

## Using exception handling along with the `int()` function to check if input is integer in Python.

The `int()` function is a pre-defined function provided by Python that is utilized to convert a number given in any base to a decimal number. The output is a number. An error is raised if the value that needs to be converted is not an integer and cannot possibly be converted into one. To tackle this, we will also use exception handling along with the `int()` function.

The exceptions that occur during the course of the program can be handled by using the `try...except` block in Python.

The following code uses exception handling along with the `int()` function to check if input is integer in Python.

The above code provides the following output:

Enter the input : 7
True

Let’s run the sample program for negative number.

Enter the input : -130
True

As you can see, this method returned true for negative number.

## Using `Regular Expression` to check if input is integer in Python.

Regular Expression, or simply RE can be utilized to check if input is integer in Python.

We will manually generate a pattern that kicks in and returns `True` whenever an integer is found in the given input string. Moreover, this custom pattern can be modified to support negative numbers as well.

The `re` library needs to be imported first in order to properly utilize regular expression in Python.

The following code uses `Regular Expression` to check if input is integer in Python.

The above code provides the following output:

Enter the input : 7
True

Let’s run the sample program for negative number.

Enter the input : -10
True

As you can see, this method returned true for negative number.

#### Code Explanation:

• The `re` library is imported to the code first.
• The input is taken from the user by using the `input()` function.
• Then, the patter is designed using the `re.compile()` function.
• The values are then compared using the `re.match()` function.
• The output is displayed and successfully provides the solution to the given problem.
##### Explanation of the pattern:
• `^ :` denotes the beginning of the string
• `\-? :` utilized to indicate that the entered could be positive or negative.
• `[1-9] :` denotes the first digit of the number. It has to be a number between 1 and 9, but it cannot be 0.
• `[0-9]* :` denotes the following digits after the first digit.
• `\$ :` denotes the termination of the string.

That’s all about how to check if input is integer in Python.

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