Hướng dẫn check string empty python

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

test_str1 = ""

test_str2 = "  "

print("The zero length string without spaces is empty ? : ", end="")

if(len(test_str1) == 0):

    print("Yes")

else:

    print("No")

print("The zero length string with just spaces is empty ? : ", end="")

if(len(test_str2) == 0):

    print("Yes")

else:

    print("No")

Output : 
 

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

test_str1 = ""

test_str2 = "  "

print ("The zero length string without spaces is empty ? : ", end = "")

if(not test_str1):

    print ("Yes")

else :

    print ("No")

print ("The zero length string with just spaces is empty ? : ", end = "")

if(not test_str2):

    print ("Yes")

else :

    print ("No")

Output :  

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

test_str1 = ""

test_str2 = "  "

print ("The zero length string without spaces is empty ? : ", end = "")

if(not (test_str1 and test_str1.strip())):

    print ("Yes")

else :

    print ("No")

print ("The zero length string with just spaces is empty ? : ", end = "")

if(not(test_str2 and test_str2.strip())):

    print ("Yes")

else :

    print ("No")

Output:  

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

test_str1 = ""

test_str2 = "  "

print ("The zero length string without spaces is empty ? : ", end = "")

if(not (test_str1 and not test_str1.isspace())):

    print ("Yes")

else :

    print ("No")

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")

Output : 
 

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)