lesson 28 Strings & Text · beginner

Clean and change text with methods

strip, lower, upper, title and replace each build a new text. startswith and endswith answer True or False. The original text never changes.

You'll be able to

Call a method with a dot, chain two methods, and store the new text it returns
Explain why name.strip() on its own line changes nothing
Clean both sides before comparing text that people typed

The idea

Text typed by people is messy. It has extra spaces, random capitals and different separators. A method is a function that belongs to a value, and you call it with a dot: city.strip().

String methods never change the text they are called on, because a Python string can't be changed at all. Each method gives back a new text, and you keep it by storing it: city = city.strip().

Run each example to see what it prints. Running examples doesn't count toward progress.

example-1.py · Tidying a typed city

city = "  new YORK "
print("[" + city + "]")
print("[" + city.strip() + "]")
print(city.strip().title())
print(city.upper().strip())
print("[" + city + "]")

example-2.py · A method on the wrong kind of value

zip_code = 48301
print(zip_code.startswith("4"))

Some methods answer a question instead of building text. startswith and endswith give back True or False. replace(old, new) swaps every match. Together they handle checks such as *is this a CSV file?* or *is this SKU in the home category?*, as long as you clean the text first.

example-3.py · Checking an uploaded file name

filename = " Sales_Q3.CSV "
clean = filename.strip().lower()
print(clean)
print(clean.endswith(".csv"))
print(filename.endswith(".csv"))
print(clean.replace("_", " ").replace(".csv", ""))

When to use it: before comparing or storing anything a person typed. Mistakes to avoid:

Calling a method without storing the result. name.strip() on its own line does nothing useful.
Cleaning only one side of a comparison.
Forgetting that replace replaces *every* match, not only the first one.

Review

A method is called with a dot, and string methods always return a new text. Store it to keep it.
strip, lower, upper, title and replace build text, while startswith and endswith answer True or False.
Clean both sides before comparing text that people typed.
Next: put values into a sentence, with control over decimals and widths, using f-strings.