String Basics Recap

Strings are sequences of characters. You already know how to create them and use basic operations like concatenation. Now let's explore Python's powerful built-in string methods that save you from writing custom logic.

text = "Hello, World!"
print(type(text))       # <class 'str'>
print(len(text))        # 13

Case Methods

text = "Hello, World!"

print(text.upper())        # HELLO, WORLD!
print(text.lower())        # hello, world!
print(text.title())        # Hello, World!
print(text.capitalize())   # Hello, world!
print(text.swapcase())     # hELLO, wORLD!

# Useful for case-insensitive comparison
user_input = "YES"
if user_input.lower() == "yes":
    print("Confirmed!")

Search and Check Methods

text = "Python is awesome and Python is fun"

# Find position of substring
print(text.find("awesome"))      # 10
print(text.find("missing"))      # -1 (not found)
print(text.index("awesome"))     # 10 (raises ValueError if not found)

# Count occurrences
print(text.count("Python"))      # 2
print(text.count("is"))          # 2

# Check start/end
filename = "report.pdf"
print(filename.startswith("report"))   # True
print(filename.endswith(".pdf"))       # True
print(filename.endswith((".pdf", ".doc")))  # True (tuple of suffixes)

Content Check Methods

print("hello123".isalnum())     # True  (letters + numbers only)
print("hello".isalpha())       # True  (letters only)
print("12345".isdigit())       # True  (digits only)
print("hello".islower())       # True  (all lowercase)
print("HELLO".isupper())       # True  (all uppercase)
print("   ".isspace())         # True  (whitespace only)

Modify and Clean Methods

# Strip whitespace (very common for user input)
dirty = "   hello world   "
print(dirty.strip())        # "hello world"
print(dirty.lstrip())       # "hello world   "
print(dirty.rstrip())       # "   hello world"

# Strip specific characters
url = "///path/to/page///"
print(url.strip("/"))       # "path/to/page"

# Replace substrings
text = "I like cats. Cats are great."
print(text.replace("cats", "dogs"))         # I like dogs. Cats are great.
print(text.replace("cats", "dogs", 1))      # Replace only first occurrence

Split and Join

These two methods are among the most useful in Python:

# Split a string into a list
sentence = "Python is a great language"
words = sentence.split()           # Split by whitespace (default)
print(words)                       # ['Python', 'is', 'a', 'great', 'language']

csv_data = "Alice,25,Engineer"
fields = csv_data.split(",")       # Split by comma
print(fields)                      # ['Alice', '25', 'Engineer']

# Limit splits
text = "one:two:three:four"
print(text.split(":", 2))          # ['one', 'two', 'three:four']

# Join a list into a string
words = ["Python", "is", "fun"]
print(" ".join(words))             # "Python is fun"
print("-".join(words))             # "Python-is-fun"
print(", ".join(words))            # "Python, is, fun"

String Slicing

text = "Python Programming"

# Syntax: string[start:end:step]
print(text[0:6])        # "Python"      (index 0 to 5)
print(text[7:])         # "Programming" (index 7 to end)
print(text[:6])         # "Python"      (start to index 5)
print(text[-11:])       # "Programming" (last 11 chars)
print(text[::2])        # "Pto rgamn"  (every 2nd char)
print(text[::-1])       # "gnimmargorP nohtyP" (reversed)

Advanced f-String Formatting

f-strings support powerful formatting beyond simple variable insertion:

# Number formatting
price = 49.99
print(f"Price: ${price:.2f}")           # Price: $49.99
print(f"Price: ${price:10.2f}")         # Price:      $49.99 (padded)

big = 1234567
print(f"Count: {big:,}")                # Count: 1,234,567

# Percentage
ratio = 0.856
print(f"Score: {ratio:.1%}")            # Score: 85.6%

# Padding and alignment
name = "Alice"
print(f"|{name:<10}|")    # |Alice     | (left-aligned)
print(f"|{name:>10}|")    # |     Alice| (right-aligned)
print(f"|{name:^10}|")    # |  Alice   | (centered)
print(f"|{name:*^10}|")   # |**Alice***| (centered with fill)

# Expressions inside f-strings
x = 10
print(f"{x} squared is {x**2}")         # 10 squared is 100
print(f"{'yes' if x > 5 else 'no'}")   # yes

Multi-line Strings

# Triple quotes for multi-line
message = """Dear User,

Thank you for signing up.
Your account is now active.

Best regards,
The Team"""

print(message)

# Raw strings (ignore escape characters)
path = r"C:\Users\name\documents"
print(path)     # C:\Users\name\documents (no escaping needed)

Practical Examples

# Clean and validate email
def clean_email(email):
    email = email.strip().lower()
    if "@" in email and "." in email.split("@")[1]:
        return email
    return None

print(clean_email("  Alice@Example.COM  "))  # alice@example.com
print(clean_email("invalid"))                 # None

# Parse a log line
log = "2026-03-04 10:30:15 ERROR Database connection failed"
parts = log.split(" ", 3)    # Split into max 4 parts
date, time, level, msg = parts
print(f"[{level}] {msg} at {date} {time}")
# [ERROR] Database connection failed at 2026-03-04 10:30:15

# Build a simple table
headers = ["Name", "Age", "City"]
rows = [
    ["Alice", "25", "London"],
    ["Bob", "30", "Paris"],
    ["Charlie", "28", "Berlin"]
]

for header in headers:
    print(f"{header:<10}", end="")
print()
print("-" * 30)
for row in rows:
    for cell in row:
        print(f"{cell:<10}", end="")
    print()

Summary

• Case: upper(), lower(), title(), capitalize()
• Search: find(), count(), startswith(), endswith(), in
• Clean: strip(), replace()
• Split/Join: split() breaks strings apart, join() combines lists
• Slicing: string[start:end:step] extracts substrings
• f-strings: Support number formatting, alignment, padding, and expressions