string contains python

In the <a href="https://python.org">Python</a> programming language, you can work with strings. A <a href="https://pythonbasics.org/strings/">string</a> is a text object in Python. If you have a large string (sentence, paragraph, chapter, book), you may want to search in it.

Searching in a large string, is known as finding a sub-string. Programming languages handle with this in different ways.

How to find a sub-string in Python?

If you programmed in other languages before, you may know string.contains() or string.indexof()

if not string.contains("word"):
   continue

Examples

Python doesn't have these, but it's not hard to find sub-strings. You can use the in keyword like this:

    >>> s = "Hello World"
    >>> if "World" in s:
    ...     print("found")
    ... 
    found
    >>>

You can use the string method .find() too

>>> if s.find("World") != -1:
...     print("Found")
... 
Found
>>>

Case sensitive

Both are case-sensitive, so this won't return anything because the first capital letter is missing:

>>> if s.find("world") != -1:
...     print("Found")
...

To avoid case-sensitive problems, you can call the lower() method on both strings.

>>> if "World".lower() in s.lower():
...     print("Found")
... 
Found

This works for different characters too, but be careful with non-English characters. Like the Portugese word for read ("lê")

>>> s = "lê"
>>> if "LÊ".lower() in s.lower():
...     print("Found")
... 
Found

But only for newest versions of Python! If you try the same in an older version of Python:

python2
Python 2.7.17 (default, Nov  7 2019, 10:07:09) 
[GCC 9.2.1 20191008] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> s = "lê"
>>> if "LÊ".lower() in s.lower():
...     print("Found")
... 
>>

To prevent problems like this, you want to rely on casefold().

>>> s = "lê"
>>> if "LÊ".casefold() in s.casefold():
...     print("Found")
... 
Found
>>>

Related links:

<a href="https://pythonbasics.org/strings/">More on Python strings</a>
<a href="https://python.org">Python official homepage</a>
<a href="https://pythonbasics.org/">Learn Python</a>