Python Strings · Working with Text

• 1. What is a string?
• 2. Basic string operations
• 3. Common string methods
• 4. String formatting (f-strings)
• 5. Escape characters
• 6. Quick reference
• 7. Quick Challenge: String Detective
• 8. Exercises
• 9. Common Errors & Solutions
• 10. Check Your Understanding
• 11. Your Progress Tracker

A string is a sequence of characters used to represent text. In Python, you can create strings using single quotes ' ' or double quotes " ".

# String examples
name = "Alice"
message = 'Hello, World!'
empty = ""
quote = 'He said "Python is fun"'
multi_line = """This is
a multi-line
string"""

# Concatenation (joining strings)
first = "Hello"
last = "World"
greeting = first + " " + last   # "Hello World"

# Repetition
laugh = "ha" * 3   # "hahaha"

# Length (how many characters?)
text = "Python"
length = len(text)   # 6

# Access characters (indexing - starts at 0!)
text = "Python"
first_char = text[0]   # 'P'
second_char = text[1]  # 'y'
last_char = text[-1]   # 'n' (negative counts from the end)

# Slicing (getting a substring)
text = "Programming"
sub = text[0:4]    # "Prog" (from index 0 up to but not including 4)
sub2 = text[4:]    # "ramming" (from index 4 to the end)
sub3 = text[:4]    # "Prog" (from start to index 4)

text = "  Hello World  "

# Case conversion
text.upper()          # "  HELLO WORLD  "
text.lower()          # "  hello world  "
text.title()          # "  Hello World  "

# Removing whitespace (very useful for cleaning user input!)
text.strip()          # "Hello World"
text.lstrip()         # "Hello World  "
text.rstrip()         # "  Hello World"

# Finding and replacing
text.find("World")    # 9 (position where "World" starts)
text.replace("World", "Python")   # "  Hello Python  "

# Checking content (returns True/False)
text.isalpha()        # False (has spaces)
"abc123".isalnum()    # True (letters and numbers)
"123".isdigit()       # True
"abc".isalpha()       # True

# Splitting and joining (very useful!)
words = "apple,banana,cherry"
fruits = words.split(",")   # ['apple', 'banana', 'cherry'] (becomes a list)
joined = "-".join(fruits)   # "apple-banana-cherry"

f-strings (Python 3.6+) are the easiest way to insert variables into strings. Just put an f before the quotes and use {variable}.

name = "Alice"
age = 25
score = 95.5

# f-string examples
message = f"My name is {name} and I am {age} years old."
print(message)   # "My name is Alice and I am 25 years old."

# You can also do calculations inside {}
print(f"Next year I will be {age + 1}.")
print(f"In 10 years, I will be {age + 10}.")

# Format numbers (control decimal places)
print(f"Your score is {score:.1f}")   # "Your score is 95.5"
print(f"Your score is {score:.0f}")   # "Your score is 96" (rounded)
print(f"Percentage: {score/100:.0%}") # "Percentage: 96%"

# Align text
print(f"{'left':<10}")   # left aligned
print(f"{'right':>10}")  # right aligned
print(f"{'center':^10}") # center aligned

Escape characters allow you to include special characters that would otherwise be hard to type.

# Common escape sequences
newline = "Line1\nLine2"      # \n = new line (line break)
tab = "Column1\tColumn2"      # \t = tab (indent)
backslash = "Path\\to\\file"  # \\ = backslash
single_quote = 'It\'s nice'   # \' = single quote inside single quotes
double_quote = "She said \"Hi\""  # \" = double quote inside double quotes

print("Hello\nWorld")
# Output:
# Hello
# World

# Raw strings (ignore escape characters - great for file paths!)
path = r"C:\Users\Name\Documents"
print(path)   # prints exactly as written, no escape issues

# CREATING STRINGS
s1 = 'single quotes'
s2 = "double quotes"
s3 = '''multi-line
string'''
s4 = r"raw\string"

# COMMON OPERATIONS
len(s)              # length
s + t               # concatenation (join)
s * 3               # repetition
s[i]                # indexing (0-based)
s[-1]               # last character
s[i:j]              # slicing (from i to j-1)
s[i:j:k]            # slicing with step

# USEFUL METHODS
s.upper()           # all uppercase
s.lower()           # all lowercase
s.strip()           # remove whitespace from ends
s.replace(old, new) # replace substring
s.split(sep)        # split into list
sep.join(list)      # join list into string
s.find(sub)         # find position (returns -1 if not found)
sub in s            # check if contains (returns True/False)

# F-STRING FORMATTING
f"value is {var}"
f"{var:.2f}"        # 2 decimal places
f"{var:>10}"        # right align width 10
f"{var:<10}"        # left align width 10
f"{var:^10}"        # center align width 10

1. How do you get the first character of a string s?
2. What does s[-1] give you?
3. How do you get the length of a string?
4. What is the difference between s.find("x") and "x" in s?
5. Why are strings called "immutable"?
6. What is an f-string and why is it useful?