EX Strings

What are Strings

Strings are sequences of characters enclosed in quotes. They can be created using single quotes (‘), double quotes (“), or triple quotes (‘’’ or “””) for strings that span multiple lines.

# Examples of strings
single_quote_string = 'Hello, World!'
double_quote_string = "Hello, World!"

Special Characters

strasse = ‘Ku’damm‘ – Error

Solution -> Backslash strasse = ‘Ku'damm’

Basis String Operations

Indexing

Strings are indexed, starting at 0. A sequence of characters is stored in a string data type. So you can access each character of a string when using [].

my_string = "Hello"
print(my_string[0]) # Output: H
print(my_string[1]) # Output: e

Concatenation (+)

Concatenation is the process of joining two or more strings together using the + operator.

greeting = "Hello"
name = "Alice"
full_greeting = greeting + ", " + name + "!"
print(full_greeting)
# Output: "Hello, Alice!"

Repetition (*)

Repetition is the process of repeating a string multiple times using the * operator.

repeat_greeting = "Hello! " * 3
print(repeat_greeting)
# Output: "Hello! Hello! Hello! "

Slicing (:)

Slicing allows you to extract a portion of a string, list, or any sequence using indices. The general syntax is:

sequence[start:end]
  • start: The index to begin the slice (inclusive).
  • end: The index where the slice ends (exclusive).
  • If start or end is omitted, Python uses the default (start = 0, end = length of sequence).

Basic Example

sample = "Hello, World!"

sample[0:5]

print(sample[0:5])  # Output: 'Hello'
  • Starts at index 0 → "H"
  • Ends before index 5 → "o"
  • Does not include the comma at index 5

sample[:5]

print(sample[:5])  # Output: 'Hello'
  • Starts from the beginning (index 0 by default)
  • Returns the first 5 characters

sample[:-1]

print(sample[:-1])  # Output: 'Hello, World'
  • Starts from the beginning
  • Ends one character before the last
  • Omits the last character "!"

Negative Indices

Python supports negative indexing:

  • -1 refers to the last element
  • -2 refers to the second-to-last, and so on

Summary Table

Expression Description
s[0:5] Characters from index 0 to 4
s[:5] First 5 characters
s[:-1] All except the last character
s[-3:] Last 3 characters
s[::2] Every second character (step = 2)

🧮 Bonus: Visual Index Map

You can visualize string indices like this:

Index:     0 1 2 3 4 5 6 7 8  9 10 11 12
String:    H e l l o ,   W o  r  l  d  !
Negative: -13          ...          -1

This helps understand how slicing selects characters based on position.

The String Function print()

Python provides several built-in methods for string manipulation.

The print() function outputs strings (or other data types) to the console. We have used that function before.

# Print a string
print("Hello, World!")
# Output: Hello, World!

# Print a string variable
message = "Hello, Python!"
print(message)
# Output: Hello, Python!

String concatenation in print() can be done using commas to separate variables or by using f-strings for more readable formatting:

print(var1, var2)        
print(f"{var1} text {var2}")

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