Seminar 003: Functions in Python¶

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Notes¶

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Functions¶

Sometimes you need to repeat the same code over and over again, and you want to avoid copy-pasting. See the example below:

Why?¶

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import math

# Task: Calculate the inverse square root of numbers 1 to 100

number_1 = 1 / math.sqrt(1)
number_2 = 1 / math.sqrt(2)
number_3 = 1 / math.sqrt(3)
number_4 = 1 / math.sqrt(4)
number_5 = 1 / math.sqrt(5)

# ... and so on

print(number_5)

# or use a for loop

for number in range(100):
    inv_sqrt = 1 / math.sqrt(number)

# Copy and past or even re-writing can be quite faulty!
# Dont let you trick from this simple example

import math # Task: Calculate the inverse square root of numbers 1 to 100 number_1 = 1 / math.sqrt(1) number_2 = 1 / math.sqrt(2) number_3 = 1 / math.sqrt(3) number_4 = 1 / math.sqrt(4) number_5 = 1 / math.sqrt(5) # ... and so on print(number_5) # or use a for loop for number in range(100): inv_sqrt = 1 / math.sqrt(number) # Copy and past or even re-writing can be quite faulty! # Dont let you trick from this simple example

Use a function¶

Python functions are a way to encapsulate code into a single unit that can be reused. These functions can take arguments and optionally return a value. Think of it as having a recipe for a cake. You can use the same recipe to make different cakes.

A function is defined using the def keyword. The function name is followed by parentheses () and a colon :. The body of the function is indented, as with Python loops and conditionals for example.

def function_name(argument: int):
    """Calculates the inverse square root of a number"""

    # Do something
    result = argument * 2

    # Return something
    return result

Here is an example of a function that calculates the inverse square root of a number:

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# Use it for any number

# Use it for a range of numbers

# Use it for any number # Use it for a range of numbers

Reasons to use functions¶

• Define it once, use it everywhere - Re-usability across applications
• Reduce overhead code - Split complex code into a series of functions
• Standardize a process - Process A requires X,Y,Z and returns A,B,C
• Share your code - Functions can be imported from your scripts

Arguments and returns¶

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# Functions can take input and return something

# Functions can take input and return something

Understanding the variable scope of functions¶

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some_variable = "Outside"
some_list = [1, 2, 3, 3]
another_variable = "Outside"


def my_function(another_variable):
    print("Calling non-argument variable: ", some_variable)
    print("Calling argument variable: ", another_variable)

    some_list.append(10)


my_function("Inside")
print("Variable outside of function: ", another_variable)
print("Changed variable: ", some_list)

some_variable = "Outside" some_list = [1, 2, 3, 3] another_variable = "Outside" def my_function(another_variable): print("Calling non-argument variable: ", some_variable) print("Calling argument variable: ", another_variable) some_list.append(10) my_function("Inside") print("Variable outside of function: ", another_variable) print("Changed variable: ", some_list)

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def take_a_number(number: str):
    # Guardian clause
    if isinstance(number, str) is False:
        raise TypeError("This requires a string!!!!")

    print(number)

def take_a_number(number: str): # Guardian clause if isinstance(number, str) is False: raise TypeError("This requires a string!!!!") print(number)

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take_a_number("10.0")

take_a_number("10.0")

Tips on using functions¶

• Keep it simple, a function should only have one job.
• Dont hesitate defining multiple small functions instead of a big one
• Include at least a brief summary of what your function is doing
• Think about generalization - How can my function be applied to deviating cases?
• Put your functions in another script and import them to reduce overhead