Python string boolean value

Python – Convert String to Boolean

In this tutorial, we will look at how to convert a string to a boolean in Python with the help of some examples.

How to convert string to a boolean in Python?

You can use the built-in bool() function to convert a string to a boolean in Python. Pass the string as an argument to the function. The following is the syntax –

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It returns True for non-empty string and False for empty strings.

Let’s look at some examples of using the above function.

# create a string s = "cat" # convert to boolean print(bool(s))

We get True as the output because the string s above is non-empty.

Let’s look at another example, this time with an empty string.

# create a string s = "" # convert to boolean print(bool(s))

We get False as the output.

Note that the result from the bool() function depends on whether the passed string is empty or not. So even if you pass truth values in string form, for example, “True” or “False”, you’ll get the same result.

# create string s1 = "True" s2 = "False" # convert to boolean print(bool(s1)) print(bool(s2))

We get True as the output for both the strings.

Convert string truth values to boolean in Python

If you want to convert a string containing truth values such as “True” or “False” to boolean, you can use the equality operator to compare them with “True” and “False” and return a boolean value.

# string to boolean function def str_to_bool(s): if s == "True": return True elif s == "False": return False else: return None # create string s1 = "True" s2 = "False" # string to boolean print(str_to_bool(s1)) print(str_to_bool(s2))

We get True for the string having the value “True” and False for the string having the value “False”.

Alternatively, if you want a more exhaustive match for a string containing truth values like “True”, “1”, “TRUE”, “true”, etc. you can use the membership operator in . Let’s look at an example.

# string to boolean function def str_to_bool(s): if s in ("True", "TRUE", "true", "1"): return True elif s in ("False", "FALSE", "false", "0"): return False else: return None # list of strings s_ls = ["True", "TRUE", "1", "False", "FALSE", "0"] # string to boolean for s in s_ls: print(str_to_bool(s))

True True True False False False

We get True as the output for the string “true”.

Note that the above example is a very specific use case. It all depends on which string values you want to consider as True and which string values you want to consider as False .

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Author

Piyush is a data professional passionate about using data to understand things better and make informed decisions. He has experience working as a Data Scientist in the consulting domain and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects. View all posts

Data Science Parichay is an educational website offering easy-to-understand tutorials on topics in Data Science with the help of clear and fun examples.

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how to convert a string to boolean in python

This article discusses a brief introduction of string and boolean datatypes. Lastly, we’ll discuss How to convert a String to Boolean in Python. The string is a derived datatype used to represent a sequence of characters. They are usually declared using quotation marks. You can use both single quotes or double quotes to declare a string.

Strings in Python are not changeable. Once created, they can’t be changed like tuples in Python. Strings are generally used to label information on graphical user interfaces or many other places like that.

On the other hand, Boolean is a built-in data type in Python that return answers in logic types 0/1, Yes/No, or true/False.

Ways to Convert String to Boolean in Python

The most important question is what is the purpose of boolean datatypes? Why do we need to convert a string to boolean. Boolean datatypes can be used to check if the input taken from the user is an empty string or non-empty. They can also be used to check if an input is an instance of a particular datatype or not

There can be several other uses also. We’ll discuss different methods along with their uses to convert a string to boolean expression.

Method 1: Conversion of string to boolean using bool() method

Python provides a builtin bool() function which takes string as an input. If the string is empty, the function returns false. For non-empty strings, it return true.

string = input("Enter a string: ") value = bool(string) if(value): print("The entered value is a string") else: print("The string entered is empty")

Enter a string: Welcome to Entechin The entered value is a string

Now press enter without typing anything, and the code will display the following output on the screen.

The string entered is empty.

Method 2: Conversion of string to boolean using strtobool() method

The distutils.util module provides strtobool() method which can be used to convert a string to a boolean value i.e., 0 or 1.The method only accepts true, false, t, f yes, no, y, n, off values. Any other value except them raises a ValueError. It converts the positive values to 1 such as true, yes etc. and converts negative values such as no, false etc.

The following code demonstrates the use of strtobool() method to convert a string to boolean.

import distutils.util as module input_value = module.strtobool("True") print("Output: ",input_value)

input_value = module.strtobool("False") print("Output: ",input_value)

input_value = module.strtobool("Hi") print("Output: ",input_value)

ValueError: invalid truth value 'hi'

Method 3: Convert a string to a boolean to check if an object is an instance of a particular type

Suppose you’re designing an application where you need an integer. To check whether the input entered by user is an integer or not, you can use boolean datatypes. If you want to know whether an object is an instance of a particular type, you can use the built-in Python function isinstance().

x = int(input("Enter a value: ")) print(isinstance(x,int))

In the above example, the data type of input is an integer. Therefore, the isinstance () returns True, but if the data type is not an integer, it returns False. Similarly, you can also check whether the input entered by the user is a string.

x = "Hello" print(isinstance(x,int))

In the example above, the “Hello” is a string but isintance() method checks whether the value stored is an integer or not. Therefore, the output is false. Now let’s see what happens if we replace int with str.

In this article, a discussion of converting a string to a boolean in Python is presented. There are different methods to do it. Two of them are discussed in detail along with examples. Let us know about your queries in the comments. If you want to learn more about Python Programming, visit Python Programming Articles.

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How does boolean operator work on string in python

result => «qwer» I can’t understand how those things work. I thought that boolean operator on string would make type error, but it didn’t. Is it something like predefined statement, for instance «a if b else c»?

6 Answers 6

Python and and or operations stop when the answer is determined and return the value of the last object scanned. They do not return True or False. I love this feature and find myself using it all the time.

Since non-empty strings count as True

True and "asdf" or absolutely_anything_here_or_following 

stops calculating when it hits the or because the answer is now determined (one of the or values is true), and returns the last thing it checked («asdf»). No further operands are even inspected.

False and "asdf" or absolutely_anything_here 

hits the or, it doesn’t know the anwser yet so continues to the next operand. As long as absolutely_anything_here is the last operation, the answer is determined and the last thing scanned is returned.

and and or work just like the familiar boolean operators — they return true if both of their operands are true and false if one of their operands are true, respectively.

They also short circuit, just like && and || .

However, in Python, where anything can be interpreted as being True or False in a boolean context, there is an additional fact — it will return the first operand that evaluated to True or evaluated to False in a boolean context, when it has enough information to stop evaluation. (This is as opposed to constructing and returning a real boolean True or False .) This is okay to do because if it is boolean evaluated it will evaluate to the boolean it would have returned if not for this fact.

Thus (note that «» is evaluated to False in a boolean context):

>>> "" and "a" '' >>> "a" and "b" 'b' >>> "a" and "" '' >>> >>> "" or "" '' >>> "a" or "" 'a' >>> "" or "a" 'a' >>> "a" or "b" 'a' >>> "" or False False >>> "" or True True >>> False and "" False 

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Python – Convert String Truth values to Boolean

Given a string list, convert the string truth values to Boolean values using Python.

Input : test_list = ["True", "False", "True", "False"] Output : [True, False, True, False] Explanation : String booleans converted to actual Boolean.

Method 1: Convert String to Boolean in Python using bool()

The bool() method in general takes only one parameter(here x), on which the standard truth testing procedure can be applied. If no parameter is passed, then by default it returns False.

Python3

Time Complexity: O(1) -> (built-in function)

Auxiliary Space: O(1)

Method 2: Convert String to Boolean in Python using eval()

Python eval() function parse the expression argument and evaluate it as a Python expression and runs Python expression(code) within the program.

Python3

Time Complexity: O(1)

Auxiliary Space: O(1)

Method 3: Convert String to Boolean in Python using list comprehension

In this, we check for just the true value, and the rest of the values are automatically converted to a False boolean.

Python3

The original list : ['True', 'False', 'True', 'True', 'False'] The converted Boolean values : [True, False, True, True, False]

Time Complexity: O(1)
Auxiliary Space: O(1)

Method 4: Convert String to Boolean in Python using map() + lambda

In this, we apply the same approach, just a different way to solve the problem. The map() is used to extend the logic of values computed by the lambda function.

Python3

The original list : ['True', 'False', 'True', 'True', 'False'] The converted Boolean values : [True, False, True, True, False]

Time Complexity: O(n)
Space Complexity: O(n)

Another Approach:

Import the ast module.
We need to use the ast module’s literal_eval function to safely evaluate the input string as a Python literal.
Define a function called convert_string_to_bool that takes a string as input.
We define a function that takes a single argument, a string containing a truth value.
This function will return a boolean value that corresponds to the input string.
Use the ast.literal_eval function to safely evaluate the input string.
We use a try/except block to catch any syntax or value errors that may occur during the evaluation.
If an error occurs, we return False.
Otherwise, we get the evaluated value from the ast.literal_eval function.
Convert the evaluated value to a boolean using the bool function.
We pass the evaluated value to the bool function to convert it to a boolean value.
Return the boolean value.
We return the boolean value that corresponds to the input string.

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