EX Strings: Functions and Methods

🧩 What is a Function?

A function is a reusable block of code that performs a specific task. You call it by its name, followed by parentheses containing any values (parameters) it needs to work with.

Python provides several built-in functions for string manipulation.

function_name(parameter1, parameter2, ...)

String Functions

print()

Displays output in the console. You can print text, variables, or multiple values by separating them with commas.

name = "Alice"
age = 25
print("Name:", name, "| Age:", age)

len()

Returns the length of a string.

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

🧩 What is a Method?

A method is similar to a function, but it is attached to an object (like a string)
and is called using dot notation (.). It performs a task that is specific to that object.

Example:

myString = "Hello"
myString.method_name(parameter1, parameter2, ...)

String Methods

replace()

Replaces parts of a string. The replace() method can take up to three parameters:

string.replace(old, new, count)
  • old: The part of the string you want to replace
  • new: What you want to replace it with
  • count (optional): How many times to replace it (from left to right)
textA = "apple apple apple"
textB = textA.replace("apple", "banana")
print(textB)  
# Output: banana banana banana

print(text.replace("apple", "banana", 1))  
# Output: banana apple apple

find()`

Searches for a substring in a string and returns the index of its first occurrence. If the substring is not found, it returns -1.

The find() method can take up to three parameters:

string.find(sub, start, end)
  • sub: The substring you want to search for
  • start (optional): The index to start the search from
  • end (optional): The index to stop the search (not inclusive)
text = "environmental informatics"

print(text.find("informatics"))   # Output: 14
print(text.find("a", 5))          # Output: 11
print(text.find("i", 5, 10))      # Output: -1

text.find(“informatics”)

“informatics” beginnt bei Index 14 text.find(“a”, 5) Suche “a” ab Index 5 → erstes “a” ist bei 11 (in “mental”) text.find(“i”, 5, 10) Bereich ist “nment” (Index 5–9) → kein “i” enthalten → -1

count()

Counts how many times a substring appears in a string.

The count() method can take up to three parameters:

string.count(sub, start, end)
  • sub: The substring you want to count
  • start (optional): The index to start counting from
  • end (optional): The index to stop counting (not inclusive)
text = "banana banana banana"
print(text.count("banana"))         # Output: 3
print(text.count("banana", 10))     # Output: 2
print(text.count("banana", 10, 20)) # Output: 1

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

text = "marburg an der lahn"
textUpper = text.upper() 
print(textUpper)       # 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

split()

Splits a string into a list, using a specified separator.

The split() method can take up to two parameters:

string.split(sep, maxsplit)
``

- **sep** *(optional)*: The delimiter to split the string on (default is any whitespace)  
- **maxsplit** *(optional)*: The maximum number of splits to perform

```python
text = "apple,banana,cherry"
textList = text.split(",")
print(textList)         # Output: ['apple', 'banana', 'cherry']

text2 = "one two three four"
print(text2.split(" ", 2))     # Output: ['one', 'two', 'three four']

Bonus - 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.

Strings are immutable.

The String Methods and Functions create a New String! → The original remains unchanged!

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