Check if a Substring is Present in a Given String in Python
By Lenin Mishra
If you prefer to watch Youtube videos over reading blogs, check out our video on Python strings here.
Given two strings, check if s1
is present in s2
.
Method 1 - Using in and not in keywords
Code
s2 = "I like Pylenin"
s1 = 'like'
print(s1 in s2)
print(s1 not in s2)
Output
True
False
Method 2 - Python String find() Method
The find()
method in Python, finds the first occurrence of a specified value in a given string. It returns the index where the substring s1
occurs.
It returns -1 if the value is not found.
The find()
method is similar to the index()
method.
Only difference - index()
method raises an exception if the value is not found.
Code
s2 = "I like Pylenin"
s1 = 'like'
print(s2.find(s1))
Output
2
The above result tells us that the like
substring first occurs at 2nd index.
Let’s check for another substring.
Code
s2 = "I like Pylenin"
s1 = 'Python'
print(s2.find(s1))
Output
-1
The above result tells us that the substring Python
doesn’t exist in s1
.
Method 3 - Python String count() Method
The count()
method returns the number of times a substring s1
appears in the string s2
. It is not case sensitive.
Syntax
string.count(value, start, end)
value: The substring to search for(required)
start: The integer position to start the search. Default is 0.(Optional)
end: The integer position to end the search. Default is the end of the string.(Optional)
Code
s2 = "I like Pylenin"
s1 = 'like'
if s2.count(s1) > 0:
print(f"'{s1}' exists in '{s2}'")
Output
'like' exists in 'I like Pylenin'
Let’s search for a non-existing string.
Code
s2 = "I like Pylenin"
s1 = 'Python'
if s2.count(s1) > 0:
print(f"'{s1}' exists in '{s2}'")
else:
print(f"'{s1}' doesn't exist in '{s2}'")
Output
'Python' doesn't exist in 'I like Pylenin'
Let’s now search a substring s1
in a specific portion of string s2
.
Code
s2 = "I like reading Pylenin blogs on Python"
s1 = 'Python'
# Search between position 10 and 20
if s2.count(s1, 10, 20) > 0:
print(f"'{s1}' exists in '{s2}'")
else:
print(f"'{s1}' doesn't exist in '{s2}'")
print(s2.find(s1))
Output
'Python' doesn't exist in 'I like reading Pylenin blogs on Python'
32
As you can see, the substring Python
doesn’t occur between the positions 10 and 20. The find()
method shows that it occurs at position 32.
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