Python String Methods for Beginners, strip, split, join, replace

Most real data arrives as text: a name typed into a form, a line from a file, a filename, an email address. Before you can do anything useful with it, you usually need to clean it up, cut it into pieces, or check what is inside. Python strings come with built-in methods for all of that. A handful of them cover almost every day-to-day need. Every example was run in Python 3, and the output shown is what it printed.

1. First, the rule that explains everything

The official documentation describes strings as immutable: once created, a string cannot be changed. Every string method that seems to modify text actually returns a new string and leaves the original alone.

name = "  Ada Lovelace  "
name.strip()
print(repr(name))
clean = name.strip()
print(repr(clean))

Output:

'  Ada Lovelace  '
'Ada Lovelace'

The second line of code did the work but threw the result away. If you want to keep the cleaned version, assign it to a variable. Forgetting this is the most common reason a string method "doesn't work."

2. strip(): remove spaces from the ends

strip() removes whitespace from the start and end of a string, which is exactly what you want for values typed into forms. lstrip() and rstrip() do only the left or right side.

You can also pass characters to remove, but read the documentation's warning carefully: the argument is a set of characters, not a word to remove.

subject = "Re: Report"
print(subject.lstrip("Re: "))
print(subject.removeprefix("Re: "))

Output:

port
Report

lstrip("Re: ") kept removing any of the characters R, e, colon and space until it hit one that was not in the set, so it ate the "Re" from "Report" too. The documentation points to removeprefix() for removing one exact prefix, which is what was intended here. There is a matching removesuffix() for endings.

3. split(): cut a string into a list

split() returns a list of pieces. It behaves differently depending on whether you give it a separator:

print("  red   green blue ".split())
print("red,,green".split(","))
print("2026-10-17 Team call: budget, hiring".split(" ", 1))

Output:

['red', 'green', 'blue']
['red', '', 'green']
['2026-10-17', 'Team call: budget, hiring']

With no argument, the documentation says runs of whitespace count as one separator and empty strings are dropped, so messy spacing disappears. With an explicit separator, two separators in a row produce an empty string between them. The second argument, maxsplit, limits how many cuts are made, which is handy for splitting a date off the front of a line.

4. join(): put a list back together

join() is the reverse of split(). The string you call it on becomes the glue between items:

colors = ["red", "green", "blue"]
print(", ".join(colors))
print(" / ".join(colors))

Output:

red, green, blue
red / green / blue

The documentation notes that join raises a TypeError if any item is not a string. Numbers trip people up:

ids = [104, 221, 309]
print(", ".join(ids))

TypeError: sequence item 0: expected str instance, int found

Convert each item first. map(str, ids) applies str() to every item:

print(", ".join(map(str, ids)))

104, 221, 309

5. replace(): swap one piece of text for another

phone = "555-010-4477"
print(phone.replace("-", ""))
print(phone.replace("-", ".", 1))

Output:

5550104477
555.010-4477

By default every match is replaced. The optional third argument limits how many.

6. lower(), upper(), and title(): fix capitalization

Comparisons in Python are exact, so "Ada@Example.COM" and "ada@example.com" are different strings. Lowercase both sides before comparing:

typed = "Ada@Example.COM"
saved = "ada@example.com"
print(typed == saved)
print(typed.lower() == saved)

False
True

title() capitalizes the first letter of each word, with a quirk the documentation calls out: apostrophes count as word boundaries.

print("o'neil's report".title())

O'Neil'S Report

Check the result before using title() on names.

7. find(), in, startswith(), endswith(): look inside

filename = "invoice_2026_final.pdf"
print(filename.find("2026"))
print(filename.find("2025"))
print("2025" in filename)
print(filename.endswith((".pdf", ".docx")))

Output:

8
-1
False
True

find() returns the position of the first match, counting from 0, or -1 if it is not found. The documentation recommends using in when you only need a yes or no answer. endswith() and startswith() accept a tuple, so one call can check several file types.

8. Putting it together

A line pasted from a spreadsheet, with stray spaces and mixed case:

line = "  Ada Lovelace , ADA@Example.com ,  London  "
name, email, city = line.split(",")
name = name.strip()
email = email.strip().lower()
city = city.strip()
print(" | ".join([name, email, city]))

Ada Lovelace | ada@example.com | London

split(",") cuts the line into three pieces, which are unpacked into three variables. Each piece is stripped, and the email is lowercased by chaining two methods. Chaining works because each method returns a new string that the next one can use.

9. Key takeaways

• Strings are immutable, so string methods return a new string; assign the result to keep it.
• strip() removes characters from a set, not a word; use removeprefix() to drop an exact prefix.
• split() with no argument handles messy whitespace; with a separator it keeps empty pieces.
• join() only accepts strings, so convert numbers with str() first.
• Use in for a yes or no check, and find() only when you need the position.