Python strings have powerful built-in methods that make text manipulation easy. Here are the most essential ones you'll use every day:

1. Case Conversion Methods

text = "Hello World"

# Convert to uppercase
text.upper()  # "HELLO WORLD"

# Convert to lowercase
text.lower()  # "hello world"

# Title case (capitalize each word)
text.title()  # "Hello World"
"hello world".title()  # "Hello World"

# Capitalize first letter only
"hello world".capitalize()  # "Hello world"

# Swap case
"Hello World".swapcase()  # "hELLO wORLD"

2. strip() - Remove Whitespace

# Remove leading and trailing whitespace ✅
text = "  hello world  "
text.strip()  # "hello world"

# Remove only from left
text.lstrip()  # "hello world  "

# Remove only from right
text.rstrip()  # "  hello world"

# Remove specific characters
"###Hello###".strip('#')  # "Hello"
"...python...".strip('.')  # "python"

# Common use: Clean user input
user_input = input().strip()  # Remove extra spaces

3. split() and join()

# Split string into list
text = "apple,banana,cherry"
fruits = text.split(',')  # ['apple', 'banana', 'cherry']

# Split on whitespace (default)
"hello world python".split()  # ['hello', 'world', 'python']

# Limit splits
"a-b-c-d".split('-', 2)  # ['a', 'b', 'c-d']

# Split lines
multiline = "line1\nline2\nline3"
lines = multiline.splitlines()  # ['line1', 'line2', 'line3']

# Join list into string ✅
words = ['hello', 'world']
' '.join(words)  # "hello world"
','.join(words)  # "hello,world"
'\n'.join(words)  # "hello\nworld"

4. replace() - Substitute Text

# Replace substring
text = "Hello World"
text.replace('World', 'Python')  # "Hello Python"

# Replace all occurrences
text = "apple apple apple"
text.replace('apple', 'orange')  # "orange orange orange"

# Limit replacements
text.replace('apple', 'orange', 2)  # "orange orange apple"

# Remove characters (replace with empty string)
"hello123world".replace('123', '')  # "helloworld"

# Chain replacements
text = "a-b-c"
text.replace('-', ' ').replace(' ', '_')  # "a_b_c"

5. find() and index() - Search

text = "Hello World"

# find() - returns index or -1 if not found ✅
text.find('World')  # 6
text.find('xyz')    # -1

# index() - returns index or raises ValueError
text.index('World')  # 6
# text.index('xyz')  # ValueError!

# Find from right
text.rfind('o')   # 7 (last 'o')
text.rindex('o')  # 7

# Check if substring exists (better than find)
if 'World' in text:
    print("Found!")

# Count occurrences
"hello world".count('l')  # 3
"banana".count('na')      # 2

6. startswith() and endswith()

# Check prefix
filename = "report.pdf"
filename.startswith('report')  # True
filename.startswith('data')    # False

# Check suffix
filename.endswith('.pdf')  # True
filename.endswith('.csv')  # False

# Multiple options (tuple)
filename.endswith(('.pdf', '.doc', '.txt'))  # True

# Practical: Filter files
files = ['data.csv', 'image.png', 'report.pdf']
csv_files = [f for f in files if f.endswith('.csv')]

# Check URL
url = "https://example.com"
if url.startswith(('http://', 'https://')):
    print("Valid URL")

7. String Formatting

# f-strings (Python 3.6+) ✅ Best!
name = "Alice"
age = 30
print(f"{name} is {age} years old")
# "Alice is 30 years old"

# Format with expressions
print(f"{name.upper()} is {age + 1} next year")

# Format numbers
price = 19.99
print(f"Price: ${price:.2f}")  # "Price: $19.99"

# .format() method
"Hello {}, you are {}".format(name, age)
"Hello {name}, age {age}".format(name="Bob", age=25)

# % formatting (old style)
"Hello %s, you are %d" % (name, age)

8. Checking String Content

# Check if alphanumeric
"Hello123".isalnum()  # True
"Hello 123".isalnum() # False (space)

# Check if alphabetic
"Hello".isalpha()     # True
"Hello123".isalpha()  # False

# Check if numeric
"12345".isdigit()     # True
"123.45".isdigit()    # False

# Check if lowercase/uppercase
"hello".islower()     # True
"HELLO".isupper()     # True

# Check if whitespace
"   ".isspace()       # True
" a ".isspace()       # False

9. Padding and Alignment

# Center text
"hello".center(10)      # "  hello   "
"hello".center(10, '*') # "**hello***"

# Left justify
"hello".ljust(10)       # "hello     "
"hello".ljust(10, '-')  # "hello-----"

# Right justify
"hello".rjust(10)       # "     hello"
"hello".rjust(10, '0')  # "00000hello"

# Zero padding for numbers
"42".zfill(5)    # "00042"
"-42".zfill(5)   # "-0042"

10. Practical Examples

# Clean and normalize email
email = "  [email protected]  "
clean_email = email.strip().lower()  # "[email protected]"

# Parse CSV line
line = "John,25,NYC"
name, age, city = line.split(',')

# Extract filename from path
path = "/home/user/documents/file.txt"
filename = path.split('/')[-1]  # "file.txt"
basename = filename.split('.')[0]  # "file"

# Create slug from title
title = "Hello World - Python Tutorial!"
slug = title.lower().replace(' ', '-').replace('!', '')
# "hello-world---python-tutorial"

# Validate password
password = "MyPassword123"
is_valid = (len(password) >= 8 and
            any(c.isupper() for c in password) and
            any(c.isdigit() for c in password))

# Parse key-value pairs
config = "name=John;age=30;city=NYC"
pairs = [pair.split('=') for pair in config.split(';')]
config_dict = dict(pairs)
# {'name': 'John', 'age': '30', 'city': 'NYC'}

Best Practices

• ✅ Use f-strings for formatting (Python 3.6+) - fastest and most readable
• ✅ Use strip() on user input to remove extra whitespace
• ✅ Use in operator instead of find() != -1
• ✅ Use join() to concatenate many strings (much faster than +)
• ✅ Use startswith()/endswith() for prefix/suffix checks
• ❌ Don't use + in loops to build strings (use list + join instead)
• ❌ Don't use index() without try/except (use find() instead)
• ⚠️ Remember: strings are immutable - methods return new strings