1.what is a function?

- a process for executing a task, reusable

- useful for re-act similar stuff

#stay DRY - Don't Repeat Yourself!

(WET - write everything twice)

#*Abstract away* code for other users

2.function structure

def name_of_function():

#block of runnable code

def say_hi():

print("what is your name?")

name = input()

print(f"hi, {name}")

say_hi()

def sing_happy_birthday():

print("Happy birthday to you")

print("Happy birthday to you")

print("Happy birthday dear you")

print("Happy birthday to you")

for i in range(2,4):

sing_happy_birthday()

3. return value for functions

#return will exit the function, anthing after return won't be touched

#return will outputs whatever value is placed after the return keyword

#return pops the function off of the call stack

def square_of_7():

return 7**2

result = square_of_7()

print(result)

from random import random

def filp_coin():

#random() generate random number 0 - 1 (no 1)

if(random() > 0.5):

return "heads"

else :

return "tails"

#print(filp_coin())

#if has the same function definination, it will overwrite and pick the bottom one

def filp_coin():

#random() generate random number 0 - 1 (no 1)

if(random() > 0.5):

return "HEADS"

else :

return "TAILS"

print(filp_coin())

#只有一个if条件时if需要在最后，这是为啥？。。

def generate_evens():

return [x for x in range(1,50) if x % 2 == 0 ]

4. function parameters

def square(num):

return num * num

print(square(4)) #16

def add(a,b):

return a + b

print(add(2,3)) #5

#it is better to make function parameter name meaningful

#parameter vs arguments

parameter is a variable in function defination

argument is the actual value of this variable that gets passed to function

5.default parameters

#give power a default value -- the thing happened to pop()

def exponent(num,power = 2):

return num ** power

print(exponent(2,3))

print(exponent(3)) #9

# the default parameter can be anything, even other functions!

eg : just the name of function, no() aftert name!

def add(a,b):

return a + b

def math(a,b,fn = add):

return fn(a,b)

def substract(a,b):

return a - b

print(math(2,3)) #5

print(math(2,3,substract)) # -1

#def math(fn = add, a,b) #error, default has to be at the end or 一路向下

#因为python是按照顺序assign para 的

6.keyword argument

#can specify the argument -- only if we know the name of parameters

print(exponent(power=2, num=5)) #25

#more expilicit, a little more flexibility

#it is useful when passing a dictionary to a function and unpacking it's values

#注意与 default para 区别

7.scope

#where the variables can be accessed

-variable created in functions are scoped in that function! --only avaiable in that function

-global not in a function

total = 0

def increment():

total += 1

return total

increment() #ERROR! local variable 'total' referenced before assignment

#it expect a local variable

total = 0

def increment():

global total #this key word will work

total += 1

return total

print(increment()) # 1

print(increment()) # 2

--nonlocal #let us modify a parent's variables in a child(AKA nested) function

def outer():

count = 0 #since count is not a gobal variable

def inner():

nonlocal count

count += 1

return count

return inner()

8. it is better to write docs for function by using ''' in a function and use function.__doc__ (are dounle underscores) to access it

def exponent(num,power = 2):

'''A simple function to calculate exps, the second para is power, default as 2'''

return num ** power

#double underscore!!!!

print(exponent.__doc__)

9.function exercise

A.

def last_element(para):

if(len(para) != 0):

return para[len(para)-1]

return None

#更简单的写法

def last_element(l):

if l:

return l[-1]

return None

B. is_pali?(空格和大小写freeB）

def is_palindrome(string):

stripped = string.replace(" ", "").upper()

return stripped == stripped[::-1]

C. 注意区别 for 和 list comprehension ，普通的for loop 没法把if写在一行

def multiply_even_numbers(l):

res = 1

for i in l :

if (i % 2 == 0) :

res *= i

return res

D.只大写首字母

def capitalize(string):

return string[0].upper()+string[1:]

E.注意区别bool和truthy

def compact(l):

return[ k for k in l if k]

#错误写法，只判断是不是等于True

def compact(l):

return[ k for k in l if k == True]

10. *args

#A special operator we can pass to a function

#gathers remaining arguments as a tuple

#just start with * (don't need to call args)

def sum_all_nums0(*args):

print(args)

sum_all_nums0(4,6) #(4, 6)

#now it will work with all numbers of arguments

def sum_all_nums(*args):

total = 0

for num in args:

total += num

return total

print(sum_all_nums(4,6,8,4)) #22

print(sum_all_nums(4,6)) #10

def sum_all_nums2(num1, num2, *args):

total = 0

for num in args:

total += num

return total

print(sum_all_nums2(4,6,8,4)) #12 -- this way num1 and num2 is ignored

print(sum_all_nums2(4,6)) #0 --empty tuple

def ensure_correct_info(*args):

if "colt" in args and "steel" in args:

return "welcome back colt"

return"who you are"

print(ensure_correct_info("hello", 78)) #who you are

print(ensure_correct_info("hello", "colt")) #who you are

print(ensure_correct_info("hello", "Colt", "steel")) #who you are --case sensitive

print(ensure_correct_info("hello", "colt", "steel")) #welcome back colt

11. **kwargs

#gathers remaining keyword arguments as a dictionary

def fav_colors(**kwargs):

print(kwargs)

for person, color in kwargs.items():

print(f"{person}'s favoarte color is {color}")

fav_colors(colt = "purp", ruby = "red", evennly = "tea") #{'colt': 'purp', 'ruby': 'red', 'evennly': 'tea'}

#传参数 colt 不可以带引号，--SyntaxError: keyword can't be an expression

'''

colt's favoarte color is purp

ruby's favoarte color is red

evennly's favoarte color is tea

'''

12.parameter ordering

1-parameters

2-*args

3-default parameters

4-**kwargs

def display_info(a, b, *args, instructor = "colt", **kwargs):

return [a,b,args,instructor,kwargs]

print(display_info(1,2,3,last_name = "steele", job = "instructor"))

#[1, 2, (3,), 'colt', {'last_name': 'steele', 'job': 'instructor'}]

#注意只有一个元素的tuple

13. use * as an argument: argument unpacking

def sum_all_values (*args):

print(args) # (1, 2, 3, 4, 5, 6)

total = 0

for num in args:

total += num

print(total)

nums = [1,2,3,4,5,6]

#sum_all_values(nums) #TypeError: unsupported operand type(s) for +=: 'int' and 'list'

#args: ([1, 2, 3, 4, 5, 6],) ---只有一个元素的tuple， num是第一个元素（list），无法与total（int）相加

#解决方法：

sum_all_values(*nums) #21

14.use ** to unpack dictionary

def display_names(first,second):

print(f"{first} says hello to {second}")

names = {"first": "colt", "second":"Rust"} #should be the name passed in para

display_names(**names) #colt says hello to Rust

#exercise: 学习get（） 的用法 --可以传两个参数：get（要查的值，是None的话设为 default）

def calculate(**kwargs):

operation_lookup = {

'add': kwargs.get('first', 0) + kwargs.get('second', 0),

'subtract': kwargs.get('first', 0) - kwargs.get('second', 0),

'divide': kwargs.get('first', 0) / kwargs.get('second', 0),

'multiply': kwargs.get('first', 0) * kwargs.get('second', 0)

}

is_float = kwargs.get('make_float', False)

operation_value = operation_lookup[kwargs.get('operation', '')]

if is_float:

final = "{} {}".format(kwargs.get('message','The result is'), float(operation_value))

else:

final = "{} {}".format(kwargs.get('message','The result is'), int(operation_value))

return final