A function is a named sequence of statements that performs a computation.
Build-in Functions: int(), float(), str(), type(), and etc.
To make your own functions, follow two steps: 1. define a function 2. call a function
def lyrics():
print("I'm okay.")
lyrics()
The first line of the function is called the header. The rest is called the body.
def repeat_lyrics():
lyrics()
lyrics()
repeat_lyrics()
I'm okay.
I'm okay.
def print_twice(bruce):
print(bruce)
print(bruce)
print_twice('Spam')
print_twice(17)
Spam
Spam
17
17
michael = 'Eric, the half a bee.'
print_twice(michael)
Eric, the half a bee.
Eric, the half a bee.
Positional Arguments
def describe_pet(type, name):
print(f"My {type}'s name is {name}.")
describe_pet('hamster', 'Harry')
describe_pet('dog', 'Willie')
My hamster's name is Harry.
My dog's name is Willie.
describe_pet('harry', 'Hamster') #Order Matters
My harry's name is Hamster.
Keyword Arguments (关键字参数)
def describe_pet(type, name):
print(f"My {type}'s name is {name}.")
describe_pet(type='hamster', name='harry')
describe_pet(name='harry', type='hamster')
Default Values
def describe_pet(name, type='dog'):
print(f"My {type}'s name is {name}.")
describe_pet(name='willie')
My dog's name is Willie.
describe_pet(name='harry', type='hamster')
#The default value has been ignored.
Example: Making an Argument Optional
def show_name(first, middle, last):
full_name=first+' '+middle+' '+last
print(full_name.title())
show_name('john','lee','hooker')
def show_name(first, last, middle=''):
if middle:
full_name=first+' '+middle+' '+last
else:
full_name=first+' '+last
print(full_name.title())
show_name('jimi', 'hendrix')
A fruitful function returns a value, while a void function performs an action but does not return a value.
To return a result from a function, we use the return statement in our function.
Return means the termination of a function. If you have two returns, only the first one will take effect.
def addtwo(a, b):
added = a + b
return added
x = addtwo(3, 5)
print(x)
8
def addtwo(a, b):
added = a + b
x = addtwo(3, 5)
print(x)
None
def addtwo(a, b):
added = a + b
print(added)
x = addtwo(3, 5)
print(x)
8
None
def addtwo(a, b):
added = a + b
print(added)
return added
x = addtwo(3, 5)
print(x)
8
8
If we want to return multiple values, the function returns a tuple.
def addtwo(a, b):
added = a + b
return a, b, added
x = addtwo(3, 5)
print(x)
(3, 5, 8)
A function can return any kind of value you need it to, including more complicated data structures like lists and dictionaries.
def build_person(first, last):
person = {1: first, 2: last}
return person
musician = build_person('jimi', 'hendrix')
print(musician)
{1: 'jimi', 2: 'hendrix'}
Module is a Python file, followed with .py
Storing Your Functions in Modules
def make_pizza(size):
print(f"Making a {size}-inch pizza")
It is saved as "pizza.py" file.
We make a separate file called making_pizzas.py in the same directory as pizza.py.
import pizza
pizza.make_pizza(16)
Importing Specific Functions
#from module_name import function_name
#from module_name import function_0, function_1, function_2
from pizza import make_pizza
make_pizza(16)
Using as to Give a Function an Alias（别名）
from pizza import make_pizza as mp
mp(16)
Using as to Give a Module an Alias
import pizza as p
p.make_pizza(16)
Importing All Functions in a Module
from pizza import *
make_pizza(16)
The asterisk in the import statement tells Python to copy every function from the module pizza into this program file. Because every function is imported, you can call each function by name without using the dot notation.
However, it's best not to use this approach when you're working with larger modules that you didn't write: if the module has a function name that matches an existing name in your project, you can get some unexpected results.
When a module named is imported, the interpreter first searches for a built-in module with that name. If not found, it then searches for a file named xxx.py in a list of directories given by the variable sys.path. sys.path is initialized from these locations:
The directory containing the input script (当前工作目录).
PYTHONPATH (a list of directory names：标准库路径，第三方库路径)
import sys
print(sys.path)
For Windows, open the anaconda prompt for anaconda, or open the cmd for original Python.
pip install pillow
#conda install pillow
For macOS, open the terminal.
pip install pillow
#conda install pillow
Uninstall the package
pip uninstall pillow
#conda uninstall pillow
List all the packages
pip list
#conda list
import math
print(dir(math))
['__doc__', '__loader__', '__name__', '__package__', '__spec__', 'acos',
'acosh', 'asin','asinh', 'atan', 'atan2', 'atanh', 'ceil', 'comb', 'copysign',
'cos', 'cosh', 'degrees', 'dist', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs',
'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'gcd', 'hypot',
'inf', 'isclose', 'isfinite', 'isinf','isnan', 'isqrt', 'lcm', 'ldexp',
'lgamma', 'log', 'log10', 'log1p', 'log2', 'modf', 'nan', 'nextafter','perm',
'pi', 'pow', 'prod', 'radians', 'remainder', 'sin', 'sinh',
'sqrt', 'tan', 'tanh', 'tau', 'trunc', 'ulp']
import math
print(math.pi)
print(math.exp(50))
print(math.sin(math.pi/2))
print(math.acos(0.5))
print(math.log(5, 20))
import random
print(random.randint(1, 10)) # 产生 1 到 10 的一个整数型随机数
print(random.random()) # 产生 0 到 1 之间的随机浮点数
print(random.uniform(1.1, 5.4)) # 产生 1.1 到 5.4 之间的随机浮点数
print(random.choice('tomorrow')) # 从序列中随机选取一个元素
print(random.randrange(1, 100, 2)) # 生成从1到100的间隔为2的随机整数
a = [1, 3, 5, 6, 7]
random.shuffle(a) # 将序列a中的元素顺序打乱
print(a)
pip install you-get
# youtube-dl
pip install freegames