Basic String Operations — PythonLessonLab

THE IDEA

Understand the concept

Strings are ordered sequences of characters. Their indexes start at 0. A slice such as text[1:4] includes the start index and stops before index 4.

Methods such as upper(), lower(), strip(), and split() return useful results. Strings are immutable, so a method that changes the appearance of text returns a new string instead of changing the original.

Index and slice text
Slice stop is excluded
String methods return new values

WORKED EXAMPLES

See it step by step

Read the code, predict the output, then compare it with the result.

01. Take two slices

PYTHON

text = "Python Lab"
print(text[:6])
print(text[-3:])

EXPECTED OUTPUT

Python
Lab

The first slice stops before index 6; the negative start counts from the end.

02. Make new strings

PYTHON

phrase = "learn python"
print(phrase.title())
print(phrase.replace("python", "coding"))

EXPECTED OUTPUT

Learn Python
learn coding

String methods return new text. The original phrase is still unchanged.

HANDS-ON

Try it in Python

Edit the example and run it. Python starts in your browser the first time you click Run.

Python console

Ready to run

text = "Python Lab"
print(text[0])
print(text[1:4])
print(text.upper())
print(text.split())
print(text)

Need input()? Add one value per line

Input lines

Ctrl / ⌘ + Enter to run

OUTPUT

Your output appears here.

Your turnChange text to "Learn Python". Print its first five characters and then print an uppercase version.

Need a hint?

Assign text = 'Learn Python'. A slice ending at 5 returns the first five characters; text.upper() returns the uppercase copy.

Complete the task and select Check task to verify your code.

KNOWLEDGE CHECK

Quick quiz

Three questions. You can change your answers and try again.

DEBUG BETTER

Typical mistakes

Everyone meets these errors. See what causes them and how to fix them.

Index outside a string

COMMON MISTAKE

word = "cat"
print(word[3])

FIX

word = "cat"
print(word[2])

What happens: IndexError because valid positive indexes are 0, 1, and 2.
The last positive index is one less than the string length.

Changing a character in place