Python program to check if string is empty or not
Python strings are immutable and hence have more complex handling when talking about its operations. Note that a string with spaces is actually an empty string but has a non-zero size. This article also discussed that problem and solution to it.
Let’s see different methods of checking if string is empty or not.
Method #1 : Using len()
Using len() is the most generic method to check for zero-length string. Even though it ignores the fact that a string with just spaces also should be practically considered as empty string even its non zero.
Python3
# Python3 code to demonstrate # to check if string is empty # using len() # initializing string test_str1 = "" test_str2 = " " # checking if string is empty print ( "The zero length string without spaces is empty ? : " , end = "") if ( len (test_str1) = = 0 ): print ( "Yes" ) else : print ( "No" ) # prints No print ( "The zero length string with just spaces is empty ? : " , end = "") if ( len (test_str2) = = 0 ): print ( "Yes" ) else : print ( "No" ) |
The zero length string without spaces is empty ? : Yes The zero length string with just spaces is empty ? : No
Method #2 : Using not
not operator can also perform the task similar to len(), and checks for 0 length string, but same as the above, it considers the string with just spaces also to be non-empty, which should not practically be true.
Python3
# Python3 code to demonstrate # to check if string is empty # using not # initializing string test_str1 = "" test_str2 = " " # checking if string is empty print ( "The zero length string without spaces is empty ? : " , end = "") if ( not test_str1): print ( "Yes" ) else : print ( "No" ) # prints No print ( "The zero length string with just spaces is empty ? : " , end = "") if ( not test_str2): print ( "Yes" ) else : print ( "No" ) |
The zero length string without spaces is empty ? : Yes The zero length string with just spaces is empty ? : No
Method #3 : Using not + str.strip()
The problem of empty + zero length string can be possibly be removed by using strip(), strip() returns true if it encounters the spaces, hence checking for it can solve the problem of checking for a purely empty string.
Python3
# Python3 code to demonstrate # to check if string is empty # using not + strip() # initializing string test_str1 = "" test_str2 = " " # checking if string is empty print ( "The zero length string without spaces is empty ? : " , end = "") if ( not (test_str1 and test_str1.strip())): print ( "Yes" ) else : print ( "No" ) # prints Yes print ( "The zero length string with just spaces is empty ? : " , end = "") if ( not (test_str2 and test_str2.strip())): print ( "Yes" ) else : print ( "No" ) |
The zero length string without spaces is empty ? : Yes The zero length string with just spaces is empty ? : Yes
Method #4 : Using not + str.isspace
Works in similar way as the above method, and checks for spaces in the string. This method is more efficient because, strip() requires to perform the strip operation also which takes computation loads, if no. of spaces are of good number.
Python3
# Python 3 code to demonstrate # to check if string is empty # using not + isspace() # initializing string test_str1 = "" test_str2 = " " # checking if string is empty print ( "The zero length string without spaces is empty ? : " , end = "") if ( not (test_str1 and not test_str1.isspace())): print ( "Yes" ) else : print ( "No" ) # prints Yes print ( "The zero length string with just spaces is empty ? : " , end = "") if ( not (test_str2 and not test_str2.isspace())): print ( "Yes" ) else : print ( "No" ) |
The zero length string without spaces is empty ? : Yes The zero length string with just spaces is empty ? : Yes
Method: Using list comprehension
Python3
string = "" x = [ "no" if len (string)> 0 else "yes" ] print (x) |
['yes']
Method: Using Bool
One approach is using the bool function. The bool function returns False for empty strings and True for non-empty strings.
Here’s an example of using the bool function to check if a string is empty or not:
Python3
# Initializing a string test_str = "" # Checking if the string is empty if not bool (test_str): print ( "The string is empty." ) else : print ( "The string is not empty." ) #This code is contributed by Edula Vinay Kumar Reddy |
The string is empty.
You can also use the bool function to check if a string is empty or not after removing any leading or trailing whitespaces using the strip method:
Python3
# Initializing a string test_str = " " # Checking if the string is empty after removing leading and trailing whitespaces if not bool (test_str.strip()): print ( "The string is empty." ) else : print ( "The string is not empty." ) #This code is contributed by Edula Vinay Kumar Reddy |
The string is empty.
Method: Using strip
Python3
#input empty with and without spaces string s = "" str = " " if s.strip(): print (f "string, string1 = '{s}', with no spaces is not empty" ) else : print (f "string, string1 = '{s}', with no spaces is empty" ) if str .strip(): print (f "string, string2 = '{str}', with spaces is not empty" ) else : print (f "string, string2 = '{str}', with spaces is empty" ) |
string, string1 = '', with no spaces is empty string, string2 = ' ', with spaces is empty
Method: Using __eq__ Method
Python3
#taking an empty string and a string with spaces only string1 = "" string2 = " " if "".__eq__(string1): print (f "string, string1 = '{string1}', with no spaces is empty" ) else : print (f "string, string1 = '{string1}', with no spaces is not empty" ) if "".__eq__(string2): print (f "string, string1 = '{string2}', with no spaces is empty" ) else : print (f "string, string1 = '{string2}', with no spaces is not empty" ) |
string, string1 = '', with no spaces is empty string, string1 = ' ', with no spaces is not empty
Method: Using “and” Operator + strip() Function
Python3
#input empty with and without spaces string string1 = "" string2 = " " if string1 and string1.strip(): print (f "string, string1 = '{string1}', with no spaces is not empty" ) else : print (f "string, string1 = '{string1}', with no spaces is empty" ) if string2 and string2.strip(): print (f "string, string2 = '{string2}', with spaces is not empty" ) else : print (f "string, string2 = '{string2}', with spaces is empty" ) |
string, string1 = '', with no spaces is empty string, string2 = ' ', with spaces is empty
The “bool” approach for checking if a string is empty or not has a time complexity of O(1), since it simply checks the truth value of the string, which is a constant time operation. The Auxiliary space is also O(1) since it only requires a single boolean variable to store the truth value of the string.
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