python_functions.rmd

---
title: "Functions"
author: "JM_Wiggins"
date: '2022-06-07'
output: html_document
---
[python.org](https://www.python.org/) 
  
## Functions
### Syntax
define using `def` keyword, semicolon after function_name() is required!
```{python eval=FALSE}
def function_name(argument1, argument2): #semicolon here
  what_to_evaluate
  return output ##when you want to send the output to another part of the code
  
def function_name2(argument1, argument2):
  what_to_evaluate  
  print(output) #when you want to show the output to a human
```
if there is no `return` or `print` the function will return `none`  
  
Note: `print` is a function you call; `return` is a python keyword  
[list of python keywords](https://www.w3schools.com/python/python_ref_keywords.asp) 
More [keyword info](https://realpython.com/python-keywords/)  
get a list of python keywords in python session:
```{python eval=FALSE}
help("keywords")
```



Function Example:
```{python}
def hyp_sq(a,b):
    sum = a**2 + b**2
    return sum


print(hyp_sq(918,846)) #to print the results to the console
```
  
Function Example with [`f-strings`](https://docs.python.org/3/whatsnew/3.6.html#pep-498-formatted-string-literals)
```{python}
def allowed_driving(name, age):
    """Print'{name}is allowed to drive' or '{name} is not allowed to drive' based on check     against the MIN_DRIVING_AGE constant"""
    MIN_DRIVING_AGE = 18
    if age >= MIN_DRIVING_AGE:
        print(f'{name} is allowed to drive')
    else: 
        print(f'{name} is not allowed to drive')
        
        
```

if `what_to_evaluate` is an `if`, `else`, `elif`, or a `for` loop a semicolon must also be included after the `what_to_evaluate`
```{python eval=FALSE}
def function_name(argument1, argument2): #semicolon here
  if what_to_evaluate: #semicolon here too
    return output 
  elif evaluate_something_else: #semicolon here too
    return different_output
  
  
```

Example:
```{python}
def animalNames(letter): #semicolon
  if letter == 'a': #semicolon
    return 'Aardvark'
  elif letter == 'b': #semicolon
    return 'Baboon'
  elif letter == 'c': #semicolon
    return 'Caracal'

  
print(animalNames('a')) #note that a had to be in '' to work
```
  
Looping through a dictionary:
```{python}
GAME_STATS = dict(sara=0, bob=1, tim=5, julian=3, jim=1)


def print_game_stats(games_won):
    """Loop through games_won's dict (key, value) pairs (dict.items)
       printing (print, not return) how many games each person has won,
       pluralize 'game' based on number.

       Expected output (ignore the docstring's indentation):

       sara has won 0 games
       bob has won 1 game
       tim has won 5 games
       julian has won 3 games
       jim has won 1 game

       (Note that as of Python 3.7 - which we're using atm - dict insert order
       is retained so no sorting is required for this Bite.)
    """
    for k, v in games_won.items():
        if v >= 2 or v == 0:
            print('{} has won {} games'.format(k, str(v)))
        else:
            print('{} has won {} game'.format(k, str(v)))
    pass
 
  
print_game_stats(GAME_STATS)
```