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Python String Methods

String methods are ready-made tools for changing and checking text, like a set of scissors, glue and rulers for words. You can make letters big, trim spaces, or swap words.

In this page:

  1. Case Conversions
  2. Stripping Whitespace
  3. Replacing Substrings
  4. Splitting and Joining
  5. Finding and Counting
Syntax
python 
string.method_name(arguments)
# e.g. string.upper(), string.replace(old, new)

Case Conversions

.lower(), .upper(), and .title() return a new string with adjusted letter casing — commonly used to normalize user input for comparison, since "Yes" and "yes" would otherwise be treated as different strings.

Example: Case Conversions

python 
text = "Yes"
print(text.lower())  # "yes"
print(text.upper())  # "YES"
print(text.title())  # "Yes"

Stripping Whitespace

.strip() removes leading and trailing whitespace from a string, while .lstrip() and .rstrip() trim only the left or right side respectively — essential for cleaning up text pasted or typed by a user that might carry stray spaces.

Example: Stripping Whitespace

python 
text = "  hello  "
print(text.strip())  # removes whitespace from both ends
print(text.lstrip())  # removes whitespace from the left only
print(text.rstrip())  # removes whitespace from the right only

Replacing Substrings

.replace(old, new) scans a string for every occurrence of old and swaps it for new, returning the modified copy — useful for tasks like sanitizing input or performing simple find-and-replace text transformations.

Example: Replacing Substrings

python 
text = "I like cats"
print(text.replace("cats", "dogs"))

Splitting and Joining

.split() breaks a string into a list of substrings wherever a separator occurs (whitespace by default), and .join() does the reverse, stitching a list of strings back together using a chosen separator between each piece.

Example: Splitting and Joining

python 
words = "a,b,c".split(",")  # breaks the string into a list wherever a comma appears
print(words)
print("-".join(words))  # stitches the list back into a string, separated by "-"

Finding and Counting

.find() searches for a substring and returns the index of its first occurrence (or -1 if it's not present), while .count() instead returns how many times that substring appears anywhere in the string.

Example: Finding and Counting

python 
text = "banana"
print(text.find("na"))  # index of the first occurrence of "na"
print(text.count("a"))  # how many times "a" appears
Related Topics

Python String Slicing · Python String Formatting · Python String Operations · Python List Methods

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Common Mistakes
  1. Calling s.upper() or s.strip() and ignoring the result, when string methods return a new string and leave s unchanged (s = s.strip()).
  2. Using s.find("x") in an if as if it returned a boolean, so a match at index 0 is falsy and -1 (not found) is truthy.
  3. Expecting split() to return a string, when it returns a list, so "a,b".split(",")[0] is needed to get one piece.
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