String length and membership test in Python

Introduction

We use string length to know how many characters are in a word or sentence. Membership test helps us check if a letter or word is inside another word or sentence.

Checking if a password is long enough before accepting it.

Finding out if a message contains a certain word.

Counting how many letters are in a name.

Seeing if a letter is part of a word.

Syntax

Python

len(string)

substring in string

len(string) gives the number of characters in the string.

substring in string checks if substring is inside string and returns True or False.

Examples

This counts the letters in "hello" and gives 5.

Python

len("hello")  # returns 5

Checks if letter "a" is in the word "apple". It is, so it returns True.

Python

"a" in "apple"  # returns True

Checks if letter "z" is in "apple". It is not, so it returns False.

Python

"z" in "apple"  # returns False

Empty string has zero characters.

Python

len("")  # returns 0

Sample Program

This program counts letters in the word "banana" and checks if letters "a" and "z" are inside it.

Python

word = "banana"
print(f"The word '{word}' has {len(word)} letters.")

letter = "a"
if letter in word:
    print(f"The letter '{letter}' is in the word.")
else:
    print(f"The letter '{letter}' is not in the word.")

letter = "z"
if letter in word:
    print(f"The letter '{letter}' is in the word.")
else:
    print(f"The letter '{letter}' is not in the word.")

Important Notes

Spaces and punctuation count as characters in length.

Membership test is case sensitive: 'A' and 'a' are different.

Summary

Use len() to find how many characters are in a string.

Use in to check if a smaller string or letter is inside a bigger string.

These tools help us understand and check text easily.