Working with Strings: Functions and Methods

Built-in String Functions

Python provides several built-in functions for string manipulation.

print()

Outputs strings (or other data types) to the console.

# 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 or f-strings:

var1 = "Hello"
var2 = "World"

print(var1, var2)  # Hello World
print(f"{var1}, {var2}!")  # Hello, World!

len()

Returns the length of a string.

length = len("Hello, World!")
print(length)  # Output: 13

str()

Converts other data types to strings.

number = 42
number_string = str(number)
print(number_string)  # Output: '42'

type()

Shows the type of a value or variable.

text = "Marburg"
print(type(text))  # <class 'str'>

zahl = 42
print(type(zahl))  # <class 'int'>

sorted()

Returns a sorted list of characters from a string.

print(sorted("Marburg"))  # ['M', 'a', 'b', 'g', 'r', 'r', 'u']

list()

Converts a string into a list of individual characters.

print(list("Marburg"))  # ['M', 'a', 'r', 'b', 'u', 'r', 'g']

Built-in String Methods

replace()

Replaces parts of a string without modifying the original.

original_string = "Hello, World!"
new_string = original_string.replace("World", "Python")
print(new_string)  # Output: Hello, Python!

strip()

Removes leading and trailing whitespace.

text = "  hello  "
print(text.strip())  # Output: hello

find() and rfind()

Find first or last occurrence of a substring.

text = "Hello, World! Hello, Python!"
print(text.find("Hello"))      # Output: 0
print(text.rfind("Hello"))     # Output: 13

count()

Counts how many times a substring appears.

text = "Hello, World! Hello, Python!"
print(text.count("Hello"))  # Output: 2

split()

Splits string into substrings based on a separator.

sentence = "Hello, World! How are you?"
words = sentence.split(" ")
print(words)
# Output: ['Hello,', 'World!', 'How', 'are', 'you?']

splitlines()

Splits string at line breaks.

multiline_string = """This is line one.
This is line two.
This is line three."""

lines = multiline_string.splitlines()
print(lines)
# Output: ['This is line one.', 'This is line two.', 'This is line three.']

upper(), lower(), title(), capitalize()

text = "marburg an der lahn"

print(text.upper())       # MARBURG AN DER LAHN
print(text.lower())       # marburg an der lahn
print(text.title())       # Marburg An Der Lahn
print(text.capitalize())  # Marburg an der lahn

join()

Joins a list of strings into one string.

words = ["Hello", "Python", "World"]
joined = " ".join(words)
print(joined)  # Output: Hello Python World

startswith() and endswith()

text = "hello world"
print(text.startswith("hello"))  # True
print(text.endswith("world"))    # True

isdigit(), isalpha(), isalnum()

print("123".isdigit())    # True
print("abc".isalpha())    # True
print("abc123".isalnum()) # True

format()

Inserts values into a string using placeholders.

name = "Alice"
age = 30
print("Name: {}, Age: {}".format(name, age))
# Output: Name: Alice, Age: 30

zfill() – Zero padding

num = "42"
print(num.zfill(5))  # Output: 00042

center() – Align text

text = "Hi"
print(text.center(10, "-"))  # Output: ----Hi----

casefold() – Aggressive lowercase conversion

print("Straße".casefold() == "strasse".casefold())  # True

📋 String Methods in Python

Method / Function Description
str.lower() Converts all characters to lowercase.
str.upper() Converts all characters to uppercase.
str.title() Capitalizes the first letter of each word.
str.capitalize() Capitalizes the first character of the string.
str.strip() Removes leading and trailing whitespace.
str.split(separator) Splits the string into a list using the specified separator.
str.join(iterable) Joins elements of a list or tuple into a single string.
str.replace(old, new) Replaces all occurrences of old with new.
str.find(substring) Returns the first index of the substring or -1 if not found.
str.rfind(substring) Returns the last index of the substring or -1 if not found.
str.count(substring) Counts the number of times a substring appears.
str.startswith(prefix) Returns True if the string starts with prefix.
str.endswith(suffix) Returns True if the string ends with suffix.
str.isdigit() Returns True if the string contains only digits.
str.isalpha() Returns True if the string contains only letters.
str.isalnum() Returns True if the string contains letters and numbers.
str.format(*args, **kwargs) Formats strings using placeholders.
str.zfill(width) Pads the string with zeros on the left, until it reaches the desired width.
str.center(width, fillchar) Centers the string using the specified fill character.
str.casefold() Aggressively lowercases the string for case-insensitive comparison.

✅ You’re now ready to work efficiently with strings in Python!

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