Additional Materials found at:
Python Functions - GeeksForGeeks
Python Functions - w3schools
Functions are a set of instructions executed whenever the function name is called. These instructions may include acting or utilising some given parameters in the function, such as a String of text, or int number. Additionally, they may provide a return value that can then be further used.
# valid example of a simple function:
# define function
def Add(a, b):
return a + b
# call function
result = Add(5, 6)Function creation can be broken down into a few major components:
- Name
- Parameters
- Instructions
- Return Value
However, when making a function the only 100% required components is a Name and some Instructions to be carried out. The example function shown below has no parameters or return value, only an instruction and name.
def HelloWorld():
print("Hello World!")
HelloWorld()But such cases are unlikely due to being restrictive in capabilities, and so primarily you are going to be using all components of functions! But lets get into a bit more detail on these components
Function names need to be unique! So they cannot be the same as anything else within the current scope (more on this in Advanced Python Info). For now, concern yourself with only the current file you are working in. Shown below are two functions, different in all aspects except name:
# Define function Add
def Add(a, b):
return a + b
# Redefining function Add!
def Add(a, b, c):
print(f"result of {a} + {b} + {c} = {a+b+c}")Despite the second definition of Add taking a different number of parameters, doing a
different instruction (print) and having no return value, the name is the same, and so it
overwrites the first definition of Add!
# This is now ok
def Add(a, b):
return a + b
def PrintAddThree(a, b, c):
print(f"result of {a} + {b} + {c} = {a+b+c}")I also suggest making sure that your function names and parameter names give the program user some insight into what they are doing. This would also benefit yourself if you ever take a break from a project for a while, and can quickly remind yourself what does what.
Parameters are the second key part of a function, acting as inputs which the function can operate on. Shown in the previous examples was parameters _a, _b, and _c. These all represent some numbers that have been given to the function to add up. For more complex functions, I would suggest utilising more suitable parameter names to more readily identify what is what:
def InsertIntoDatabase(dataBase, recordList):
for record in recordList:
freeIndex = len(dataBase)
dataBase.loc[freeIndex] = recordHere, dataBase and recordList both clearly set out what is expected to be passed to the function, and should work towards minimising errors when debugging or using the function.
Default values can also be set for parameters, using an assignment:
def GetMenuSelection(menuOptions = None, inputPrompt = "Enter Input: "):
if menuOptions is None:
menuOptions = ["Yes", "No"]
print("::: User Menu :::")
for option in menuOptions:
# prints out option
print("- " + option)
# get input
return input(inputPrompt)
GetMenuSelection(inputPrompt="Please Enter an Input:")Default parameters allow the function to not require explicitly set parameters when calling, but are overwritten whenever the parameter is specified. It is important to note that any parameter with a default argument must come at the end of the list of parameters, as any parameter after that must also have a default argument. The example below would hence be invalid:
def GetMenuSelection(menuOptions = None, inputPrompt):
if menuOptions is None:
menuOptions = ["Yes", "No"]
print("::: User Menu :::")
for option in menuOptions:
# prints out option
print("- " + option)
# get input
return input(inputPrompt)
GetMenuSelection(inputPrompt="Please Enter an Input:")As for why = None is being used here instead of assigning to the list, well its best
I let you read up on it through this StackOverflow post
but dont worry about it too much. It just might explain some odd behaviour you see around
though!
Not much to say about this. These are just what is done by the function. Make sure they are clear and understandable to make for easier debugging!
Functions having return values just means you need to take a little extra care to make sure you store or utilise their outputs properly:
def Add(a, b):
return a+b
# stored correctly for later use
result = Add(5, 6)
# return value is lost
Add(7, 11)Functions should be defined before any usages within code, otherwise python wont know what the function being called is supposed to do. Typically this will be highlighted with a helpful error message to let you know.
# invalid code:
# call function
result = Add(5, 6)
# define function
def Add(a, b):
return a + b Additionally, make sure that all required parameters of a function are being passed to it correctly. Here both _a and _b are required values, with no preset defaults. Hence they are both required, else the program will fail.
def Add(a, b):
return a + b
result = Add(5)Also, when looking to create functions, you are looking to break up and modularise sections of the program. Take for instance a case where you have a bunch of repeated copy-pasted complex code thats used multiple times in a program. Should it turn out that the code actually has a bug, that could result in you having to fix multiple separate instances of the same code. Instead you can have a singular function - meaning that a bug in the function only needs to be fixed once!
# first input
print("::: User Menu :::")
options = ["Option 1", "Option 2"]
for option in options:
# prints out option
print("- " + option)
resultOne = input("selection: ")
# second input
print("::: User Menu :::")
options = ["Option 3", "Option 4", "Option 5"]
for option in options:
# prints out option
print("- " + option)
resultTwo = input("selection: ")
# Instead of separate copies of code getting a user input:
# turn into a function:
def GetMenuSelection(menuOptions, inputPrompt):
print("::: User Menu :::")
for option in menuOptions:
# prints out option
print("- " + option)
# get input
return input(inputPrompt)