How to convert int to string python
How to convert int to string python
Converting Integer to String in Python
Table of Contents
Quick Fix: Python’s built-in str(x) method converts an integer object x to a string object by using the x.__str__() method.
❖ Introduction
Problem Formulation: Given a string object in Python, what are the ways to convert it to an Integer type?
Example:
Output:
Let us have a look at an example where converting an integer becomes a defining factor in your code.
Scenario: Concatenate a string and an integer.
Actual Output:
Explanation: The usage of the + operator to concatenate a string and integer is not allowed in Python. Thus, Python throws a TypeError: unsupported operand type(s) for +: ‘int’ and ‘str’ in this case.
The solution to this problem is to convert the integer object to a string object and then concatenate the two strings as shown in the solution below.
Solution:
Before moving on to the solutions, I highly recommend you to go through the type conversion techniques explained in this tutorial.
Now, without further ado, let us dive into the solutions to our mission-critical question – “How to convert an integer to a string in Python?“
➤ Method 1: Using The str() Method
Python’s built-in str(x) function converts the object x to a string using the x.__str__() method or, if non-existent, the repr(x) built-in function to obtain the string conversion.
Python int to string format conversion
Introduction
Today, we are going to discuss how to convert numbers to strings and visa versa. It is a straightforward Python topic but it is important as well. There are various real life scenarios where type conversion is required. Before elaborating more, let us mention two example use cases to get a taste of what that means…
Reading numbers from file in python
Assume we have a text file (call it numbers.txt) where each line contains a number. For example…
We want to calculate the total sum of all numbers in the file. We can do that as follows…
In Python, reading lines from a text file produces a string data type. As you can see in the code snippet above, we had to convert the number in each line to integer so that we can compute the total sum. Let us take another example…
String int concatenation in python
Stitching strings and numbers together is a common use case in most programming language. For example, if we want to generate user ids from student names and numbers then we need to do the proper conversion. Here is an example…
In the code snippet above, we cannot simply concatenate a string to a number. The number has to be converted to a string first otherwise, an exception is raised. You can try it yourself by running the code snippet without any conversion. This brings us to the next section…
Dynamically vs statically typed languages
Python is a dynamically typed programming language. This means that we do not need to explicitly specify variable types. It is a convenient language feature but we should not be ignorant about it. The fact that Python interpreter detects variable types at runtime is true however if there is a type mismatch, an exception is raised. You might be wondering how on earth this is relevant to the main topic? Well, whenever we do type conversion (ex. subtracting two numbers in string format) we might encounter runtime errors due to type mismatch. Moral of the story, we must be careful when dealing with numbers and strings in Python. On the other hand, statically typed languages (ex. C++) would not approve any operation using incompatible types. The code does not even compile in the first place. The debate of which is better: a dynamically or statically typed language is beyond the scope of this article. Let us proceed with our discussion…
Conversion, casting and parsing
Since we are talking about type conversion, it would be relevant to point out that the terms casting and parsing refer to the same thing (i.e. conversion) one way or another.
Convert Strings to Numbers and Numbers to Strings in Python
Introduction
Before we get in to converting strings to numbers, and converting numbers to strings, let’s first see a bit about how strings and numbers are represented in Python.
Note: For simplicity of running and showing these examples we’ll be using the Python interpreter.
Strings
String literals in Python are declared by surrounding a character with double («) or single quotation (‘) marks. Strings in Python are really just arrays with a Unicode for each character as an element in the array, allowing you to use indices to access a single character from the string.
For example, we can access individual characters of these strings by specifying an index:
Numerics
Floats have unlimited length as well, but a floating-point number must contain a decimal point.
Complex numerics must have an imaginary part, which is denoted using j :
Converting Strings to Numerics
Using the int() Function
If you want to convert a string to an integer, the simplest way would be to use int() function. Just pass the string as an argument:
This same exception will even be raised if a valid float string is passed:
The int() function does have another useful feature than just converting strings to integers, it also allows you to convert numbers from any base to a base 10 integer. For example, we can convert the following binary string to a base 10 integer using the base parameter:
The same can be done for any other base, like hexadecimal (base 16):
Using the float() Function
Converting string literals to floats is done via the float() function:
The float() function offers a bit more flexibility than the int() function since it can parse and convert both floats and integers:
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However, it will raise an exception if a non-numeric value is passed to it:
While float() does not have the ability to convert non-base 10 numbers like int() does, it does have the ability to convert numbers represented in scientific notation (aka e-notation):
Using the complex() Function
Like the float() function, complex() is also more relaxed in the types of numbers it allows. For example, the imaginary part of the number can be completely omitted, and both integers and floats can be parsed as well:
As you can see, however, this should not be used as a more flexible replacement for int / float since it automatically adds the imaginary part of the number to the stringified version.
Converting Numerics to Strings
Using the str() Function
The str() function can be used to change any numeric type to a string.
The nice thing about str() is that it can handle converting any type of number to a string, so you don’t need to worry about choosing the correct method based on what type of number you’re converting.
Using the format() Function
Another way of converting numerics to strings is using the format() function, which allows you to set placeholders within a string and then convert another data type to a string and fill the placeholders.
Here’s an example:
Conclusion
Python Int to String with Leading Zeros
Challenge: Given an integer number. How to convert it to a string by adding leading zeros so that the string has a fixed number of positions.
In all methods, we assume that the integer has less than 5 characters.
Table of Contents
Method 1: Format String
The first method uses the format string feature in Python 3+. They’re also called replacement fields.
The code f’
Method 2: zfill()
Another readable and Pythonic way to fill the string with leading 0s is the string.zfill() method.
The method takes one argument and that is the number of positions of the resulting string. Per default, it fills with 0s.
You can check out the following video tutorial from Finxter Adam:
Method 3: List Comprehension
Many Python coders don’t quite get the f-strings and the zfill() method shown in methods 2 and 3. If you don’t have time learning them, you can also use a more standard way based on string concatenation and list comprehension.
You first convert the integer to a basic string. Then, you create the prefix of 0s you need to fill it up to n=5 characters and concatenate it to the integer’s string representation. The asterisk operator creates a string of 5-len(s3) zeros here.
Where to Go From Here?
Enough theory. Let’s get some practice!
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Python string to int and int to string
In this article, we will understand the conversion of Python String to Int and int to string conversion. In Python, the values are never implicitly type-casted. Let’s find out how to explicitly typecast variables.
1. Python String to int Conversion
Python int() method enables us to convert any value of the String type to an integer value.
Syntax:
Example:
Output:
Conversion of Python String to int with a different base
Python also provides us with an efficient option of converting the numbers/values of the String type to integer values under a particular base in accordance with the number system.
Syntax:
Example:
In the above snippet of code, we have converted ‘100’ to the integer value with base 8 and base 16 respectively.
Output:
ValueError Exception while Python String to int conversion
Scenario: If any of the input string contains a digit that does not belong to the decimal number system.
In the below example, if you wish to convert string ‘A’ to an integer value of A with base 16 and we do not pass base=16 as an argument to the int() method, then it will raise ValueError Exception.
Because even though ‘A‘ is a hexadecimal value, still as it does not belong to the decimal number system, it won’t consider A to be equivalent to decimal 10 unless and until we don’t pass base = 16 as an argument to the int() function.
Example:
Output:
Converting a Python list of Integer to a list of String
Python list containing integer elements can be converted to a list of String values using int() method along with List Comprehension.
Example:
Output:
2. Python int to String Conversion
Python str() method enables us to convert any value of the integer type to an String value.
Syntax:
Example:
Output:
Conclusion
In this article, we have understood the conversion of Python String to Integer and vice-versa.