Lesson 1
Exploring the Galaxy of Python Strings: Understand Basic String Operations
Introduction and Overview

Welcome to our journey into Python strings! Today, we will delve into string operations, such as concatenation and slicing, and explore a variety of essential built-in string methods available in Python. By the end of your journey, you will have mastered these operations.

Understanding Strings in Python

In Python, a String is a sequence of characters. You can define them using single ('), double ("), or triple (''' or """) quotes for multiline strings:

Python
1str1 = "Hello, Python!" 2str2 = 'Strings are fun.' 3str3 = """This is a 4Multiline 5String."""

Like lists, strings in Python have indices that start at 0.

String Concatenation

Concatenation links strings together, much like joining links in a chain. Python uses the '+' and '+=' operators for concatenation:

Python
1str1 = 'Hello' 2str2 = 'World' 3merged_str = str1 + ', ' + str2 + '!' 4merged_str += ' See?' 5 6print(merged_str) # prints "Hello, World! See?"

Note: The '+' operator is used only to join strings.

Slicing Strings in Python

Slicing in Python is akin to slicing a loaf of bread — you take a piece from the whole. The syntax is pretty simple: str[start:end] that takes a slice from start to end, with start inclusive and end exclusive. For example:

Python
1message = 'Python Programming is fun!' 2slice_message = message[7:18] # Includes characters on positions 7, 8, ..., 17 3 4print(slice_message) # Prints 'Programming'
Working with String Methods

Python is equipped with various string methods, such as:

  • str.upper() - converts all string letters to uppercase.
  • str.lower() - converts all string letters to lowercase.
  • str.replace(from, to) - replaces all occurrences of from to to.
  • str.index(sub) - searches the index of the first occurrence of the provided substring sub.
  • str.join(e1, e2, ...) - joins all provided strings e1, e2, ... with a provided separator str.
  • str.split(separator) - splits the provided string into multiple parts by the provided separator.
  • len(str) - returns the length of the string str.
  • str * <number> - repeats the str multiple times (number times).

Here's an example of how they work:

Python
1text = "Hello, World!" 2 3print(text.upper()) # prints "HELLO, WORLD!" 4print(text.lower()) # prints "hello, world!" 5print(text.replace('Hello', 'Hi')) # prints "Hi, World!" 6print(text.index('World')) # prints 7 7print(', '.join(['Hello', 'World', '!', 'How', 'are', 'you', '?'])) # prints "Hello, World, !, How, are, you, ?" 8print(text.split(", ")) # prints ["Hello", "World!"] 9print(len(text)) # prints 13 10print(text * 3) # prints "Hello, World!Hello, World!Hello, World!"
Handling Special Strings in Python

Python recognizes special escape sequences, such as \n (newline), \t (tab), and \\ (backslash). Here's a quick demonstration:

Python
1str_with_escape_sequences = "Hello\nWorld!\tEnjoy Python Programming.\\" 2print(str_with_escape_sequences) 3""" 4Prints: 5Hello 6World! Enjoy Python Programming.\ 7"""

The message appears on two lines because \n introduces a new line. \t adds a tab space, and to print a single backslash, we use \\.

Lesson Summary

Fantastic job! You've tackled Python string operations, learned about a variety of essential methods, and got acquainted with Python's special escape sequences. Practicing these will surely enhance your Python skills. Prepare for upcoming lessons on string formatting and interpolation. Onward!

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