Seminar 003: Functions in Python¶

---

Notes¶

In [1]:

# Merging dictionaries
dict1 = {"Hello": "World"}
dict2 = {"Foo": "Bar"}

merged = {}
dict_list = [dict1, dict2]

for entry in dict_list:
  for key, value in entry.items():
    merged[key] = value

merged

# Merging dictionaries dict1 = {"Hello": "World"} dict2 = {"Foo": "Bar"} merged = {} dict_list = [dict1, dict2] for entry in dict_list: for key, value in entry.items(): merged[key] = value merged

Out[1]:

{'Hello': 'World', 'Foo': 'Bar'}

In [2]:

# Pythonic merging of dictionaries
dict1 = {"Hello": "World"}
dict2 = {"Foo": "Bar"}

merged = {
    **dict1,
    **dict2,
}

merged

# Pythonic merging of dictionaries dict1 = {"Hello": "World"} dict2 = {"Foo": "Bar"} merged = { **dict1, **dict2, } merged

Out[2]:

{'Hello': 'World', 'Foo': 'Bar'}

In [6]:

# Pythonic way of merging lists
list1 = [1,2,3,4]
list2 = [5,6,7,8]

all_list = [*list1, *list2]
all_list

# Pythonic way of merging lists list1 = [1,2,3,4] list2 = [5,6,7,8] all_list = [*list1, *list2] all_list

Out[6]:

[1, 2, 3, 4, 5, 6, 7, 8]

Functions¶

Why?¶

In [7]:

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

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

print(number_5)

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 # Copy and past or even re-writing can be quite faulty! # Dont let you trick from this simple example print(number_5)

0.4472135954999579

Use a function¶

In [8]:

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

    result = 1 / math.sqrt(number)

    return result

def get_inverse_square_root(number: int): """Calculates the inverse square root of a number""" result = 1 / math.sqrt(number) return result

In [10]:

inv_sqrt = get_inverse_square_root(19892)
print(inv_sqrt)

inv_sqrt = get_inverse_square_root(19892) print(inv_sqrt)

0.007090237366685696

In [ ]:

for i in range(1, 100):
    inv_sqrt = get_inverse_square_root(i)
    print(inv_sqrt)

    # "0.3456\n"
    # do something else

for i in range(1, 100): inv_sqrt = get_inverse_square_root(i) print(inv_sqrt) # "0.3456\n" # do something else

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¶

In [12]:

# Functions can take input and return something
def my_function(arguments):
    # do something
    print("Inside function has arguments: ", arguments)
    return "something"

returned= my_function("Hello")
print("Function returned: ", returned)

# Functions can take input and return something def my_function(arguments): # do something print("Inside function has arguments: ", arguments) return "something" returned= my_function("Hello") print("Function returned: ", returned)

Inside function has arguments:  Hello
Function returned:  something

Understanding the variable scope¶

In [13]:

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)

Calling non-argument variable:  Outside
Calling argument variable:  Inside
Variable outside of function:  Outside
Changed variable:  [1, 2, 3, 3, 10]

In [16]:

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

    print(number)

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

In [18]:

take_a_number("10.0")

take_a_number("10.0")

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