#We are going to wrap back around to lists and loops

#but first functions

#functions are the only way to build scalable code

########## HOW TO CREATE A FUNCTION ##########

#This one is simple, but we go on.

def greet():

print("hello")

print("Welcome, Caleb")

#invoke

greet()

#Can invoke numerous times:

greet()

greet()

#Benefits: We can save lines of code if function is large

#One source of truth. No repeat of code. Need changes?

#update one spot

#Can improve code readability

########## Arguments and Parameters ##########

#parameter is a variable used within a function

def greet(name): #name is a parameter

print("hello")

print("Welcome, " + name)

greet("Sabrina") #Sabrina is an argument (value passed in to parameter variable)

#We can also use variables as arguments

new_guy = "Carl"

greet(new_guy)

#This gives the value "Carl" to the name parameter

########## RETURN ##########

#We can return (exit) from a function in certain situations

def greet(name):

if name == "Claire":

return

else:

print("hello")

print("Welcome " + name)

greet("Claire") #NOPE!

greet("Clarice") #YES!

#This code can be simplified by removing the else:

def greet(name):

if name == "Claire":

return

print("hello")

print("Welcome " + name)

#The concern without an else is that the line after the if is announced regardless of name

#This works, however, because there is never a case where name == "Claire" that is not returned

#We only need else if we are not returning!

########## RETURN VALUES ##########

#instead of printing inside the function, we can use the function to generate a message

#We can print outside of the function on the caller side

#caller side --> Where we invoke the function

def greet(name):

if name == "Claire":

return "Go away"

return "Hello " + name + "! Welcome to my app."

returned = greet("Sal")

print(returned)

#We can use the returned value directly...

print(greet("Claire"))

########## DEFAULT ARGUMENTS ##########

#We may want to create a method that does not require an input

def greet(name="User"):

if name == "Claire":

return "Go away"

return "Hello " + name + "! Welcome to my app."

print(greet()) #No name? Default to User

########## MULTIPLE ARGUMENTS / PARAMETERS ##########

def greet(name="User", be_nice=False):

if be_nice:

return "Hello " + name + "! Welcome to my app."

return "Go away " + name

print(greet("Caleb", True))

print(greet("Caleb"))

########## KEYWORD ARGUMENTS ###########

#This will showcase how to skip any particular parameter

def greet(name="User", be_nice=False):

if be_nice:

return "Hello " + name + "! Welcome to my app."

return "Go away " + name

print(greet(be_nice=True))

#NOTE if a parameter does not have a default value, you must specify it

#Either in order without a name, or assigning by name

########## POSITIONAL OR KEYWORD ARGUMENTS ##########

#With the function we have defined, we can pass arguments by position or by keyword

def greet(name, be_nice):

if be_nice:

return "Hello " + name + "! Welcome to my app."

return "Go away " + name

print(greet("Positional", True)) #Positional

print(greet(be_nice=True, name="Keyword")) #Keyword (NOTICE ORDER!)

#Positional arguments must follow keyword arguments

#ERROR:

#print(greet(be_nice=True, "Keyword"))

#NOTE that we can invoke by position or keyword. We can restrict to either though.

#If we want our method to have to be invoked using position, we can do that

#We can also restrict to keyword only as well.

########## POSITIONAL-ONLY ARGUMENTS ##########

def greet(name, be_nice, /): #Anything before the / must be positional

if be_nice:

return "Hello " + name + "! Welcome to my app."

return "Go away " + name

print(greet("positional", False))

#ERROR because invoking with keyword:

#print(greet("Positional", be_nice=True))

#We can also put the / between arguments

def greet(name, /, be_nice):

if be_nice:

return "Hello " + name + "! Welcome to my app."

return "Go away " + name

print(greet("Positional", be_nice=True)) #This works now.

print(greet("Positional", True)) #This works too.

#We can invoke with be_nice being named or positional

#Doesn't add a lot of value but nice when we have lots of arguments

#ERROR because invoking name by keyword:

#print(greet(name="Keyword", be_nice=True))

########## KEYWORD-ONLY ARGUMENTS ##########

#Place a *, before any arguments that are keyword-only

def greet(name, /, *, be_nice ): #be_nice is keyword only

if be_nice:

return "Hello " + name + "! Welcome to my app."

return "Go away " + name

print(greet("Positional", be_nice=True)) #be_nice= is required

#ERROR because positional

#print(greet("Positional", True))

########## SPECIAL PARAMETER SUMMARY ##########

#We've learned about positional-only arguments, and keyword-only arguments

#And of course the arguments that can be either.

#Here is full (but contrived) example

def do_nothing(pos1, pos2, pos3, /, either1, either2, *, keyword1, keyword2, keyword3):

print("pos1", pos1)

print("pos2", pos2)

print("pos3", pos3)

print("either1", either1)

print("either2", either2)

print("keyword1", keyword1)

print("keyword2", keyword2)

print("keyword3", keyword3)

do_nothing(1, 2, 3, 4, either2=5, keyword3=6, keyword1=7, keyword2=8)

#A very helpful rule to remember the positioning of this junk

#You must always invoke a method passing positional first

#Because if you passed them later, the position would be janked up

#The either parameters must be in the middle because they can also be positional

#The keyword are always last because you can mix their order

########## LIST PARAMETERS / FUNCTION TO ITERATE LIST #########

def greet_all(people):

for person in people:

print("Hello " + person)

people = ["Caleb", "Josh", "Austin"]

greet_all(people)

########## UNLIMITTED ARGUMENTS / PACKING ##########

#What if you are working with individual pieces of data?

#We can modify the function to "pack" the data with *

def greet_all(*people):

for person in people:

print("Hello " + person)

greet_all("Caleb", "Josh", "Austin")

########## UNPACKING ##########

def print_info(name, age, email):

print(name + " is " + str(age) + ". Reached at " + email)

info = ["Caleb", 12, "email@email.com"]

print_info(*info)

########## FUNCTIONS CALLING FUNCTIONS ##########

#Let's say we have this method and no way to edit it

def greet(name, be_nice=True):

if be_nice:

return "Hello " + name + "! Welcome to my app."

return "Go away " + name

#We can utilize it.

def greet_all(people):

for person in people:

print(greet(person)) #because it returns string

people_to_greet = ["Johnny", "Jimmy", "Jacob"]

greet_all(people_to_greet)