Python strings

Python Strings: Basics, Concatenation, and Repetition

This document provides an introduction to Python strings, covering their definition, creation, basic operations like concatenation and repetition, and how to measure their length.

Learning Outcomes

• Define: Understand strings as sequences of characters used to store text.
• Manipulate: Learn to join strings using concatenation and repeat them using repetition.
• Measure: Use built-in functions to find the length of any text block.

What are Strings?

In Python, a string is simply a sequence of characters wrapped in quotes. They are fundamental for processing textual data and form the foundation of user interaction.

Creating Strings

Python offers three main ways to enclose your text:

• Single Quotes: `'Hello'`
• Double Quotes: `"Python"`
• Triple Quotes: `"""Multi-line"""` (useful for multi-line strings)

Note: Quotes must match at the beginning and end!

Concatenation

Concatenation is the process of joining two or more strings together to create a new one.

• In Python, we use the + operator.
• Example:

  first = "Lego"
  second = "Blocks"
  result = first + second
  # result is "LegoBlocks"

The "No Space" Rule (Important Tip)

The + operator does not add spaces automatically. You must add them yourself!

• Example:

  name = "Alice" + " " + "Smith"
  # Output: "Alice Smith"

Repetition

Repetition creates multiple copies of a string and joins them together.

• We use the * operator followed by an integer.
• Example:

  laugh = "Ha! "
  print(laugh * 3)
  # Output: "Ha! Ha! Ha! "

The `len()` Function

The len() function counts the number of characters in a string.

• Crucial: It counts spaces and punctuation marks too!
• Example:

  text = "Hello World!"
  print(len(text)) # 12

  (The string "Hello World!" has 12 characters, including the space and exclamation mark.)

String Operators Summary

Avoid the TypeError

• Mixing Types: You cannot add a string and a number directly.
  • "Age: " + 20 → Error!
• The Fix: Convert the number to a string first using str().
  • "Age: " + str(20) → "Age: 20"

Predict the Output!

1. "5" + "5"

   Answer: "55" (Concatenates the string "5" with the string "5")

2. "Go!" * 2

   Answer: "Go!Go!" (Repeats the string "Go!" two times)

3. len("Python 3")

   Answer: 8 (Counts all characters, including the space)

Next Steps

Strings are the foundation of all user interaction in Python. The next chapter will cover String Slicing and Formatting, providing more advanced techniques for manipulating textual data.