Python How To Find Substring In String

Python provides the tools to easily find a substring inside a string. You can do this with the find() function or you could use a regex. We are going to talk about regexes a little further on in this guide but using a regex is actually my preferred way of doing things.

You can use the find() function to find a substring inside a string. This will return the index at which the substring is found.

Here is an example:

string1 = "This is my big string with words like octopus, zebra, and sardine."
x = string1.find('octopus')
print( x)

This would output: 38

To test whether or not a value was found you could use this:

if string1.find('octopus') > -1:
    print("found")
else:
    print("nothing...")

You can also specify a starting index to start searching at like this:

x = string1.find('is', 5)
print( x)                

You could specify an ending index like this if you only want to search in this range.

x = string1.find('is', 5, 25)
print( x)                

Python - Find a Substring using Regex

You can also find a substring using a regex.

string1 = "This is my big string with words like octopus, zebra, and sardine."
m = re.search("(octopus)", string1)
if m:
    print( m.groups(1) )

This should print the following:

('octopus',)

You can also use a regex to find multiple substrings inside a string.

string2 = "There is a rock on the rocky mountain but there has been no rockslide."
m = re.findall('(rock\w*)', string2)
print(m)

This would give us the output:

['rock', 'rocky', 'rockslide']