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无参数函数 ​

python
# 函数可以在没有参数的情况下声明
def generate_full_name ():
  first_name = 'he'
  last_name = 'fang'
  space = ' '
  full_name = first_name + space + last_name
  print(full_name)
generate_full_name () # calling a function

def add_two_numbers ():
  num_one = 2
  num_two = 3
  total = num_one + num_two
  print(total)
add_two_numbers()

函数有返回值 ​

python
# 函数没有return语句，则函数的值为None
def generate_full_name ():
  first_name = 'he'
  last_name = 'fang'
  space = ' '
  full_name = first_name + space + last_name
  return full_name
print(generate_full_name())

def add_two_numbers ():
  num_one = 2
  num_two = 3
  total = num_one + num_two
  return total
print(add_two_numbers())

带参数的函数 ​

python
# 单参数
def greetings (name):
  message = name + ', welcome to Python for Everyone!'
  return message

print(greetings('he'))

def add_ten(num):
  ten = 10
  return num + ten
print(add_ten(90))

def square_number(x):
  return x * x
print(square_number(2))

def area_of_circle (r):
  PI = 3.14
  area = PI * r ** 2
  return area
print(area_of_circle(10))

def sum_of_numbers(n):
  total = 0
  for i in range(n+1):
    total+=i
  print(total)
print(sum_of_numbers(10)) # 55
print(sum_of_numbers(100)) # 5050
python
# 两个参数
def generate_full_name (first_name, last_name):
  space = ' '
    full_name = first_name + space + last_name
    return full_name
print('Full Name: ', generate_full_name('Asabeneh','Yetayeh'))

def sum_two_numbers (num_one, num_two):
  sum = num_one + num_two
  return sum
print('Sum of two numbers: ', sum_two_numbers(1, 9))

def calculate_age (current_year, birth_year):
  age = current_year - birth_year
  return age

print('Age: ', calculate_age(2021, 1819))

def weight_of_object (mass, gravity):
  weight = str(mass * gravity)+ ' N' # the value has to be changed to a string first
  return weight
print('Weight of an object in Newtons: ', weight_of_object(100, 9.81))

传递带有键和值的参数 ​

python
# 传递带有key和value的参数,那么参数的顺序并不重要
def print_full_name(first_name, last_name):
  space = ' '
  full_name = first_name  + space + last_name
  print(full_name)
print(print_full_name(first_name = 'he', last_name = 'fang'))

def add_two_numbers (num1, num2):
  total = num1 + num2
  print(total)
print(add_two_numbers(num2 = 3, num1 = 2)) # Order does not matter

函数的返回值 ​

python
# 返回一个字符串
def print_name(first_name):
  return first_name
print_name('he') # he

def print_full_name(first_name, last_name):
  space = ' '
  full_name = first_name  + space + last_name
  return full_name
print_full_name(first_name='he', last_name='fang')
python
# 返回一个数字
def add_two_numbers (num1, num2):
  total = num1 + num2
  return total
print(add_two_numbers(2, 3))

def calculate_age (current_year, birth_year):
  age = current_year - birth_year
  return age
print('Age: ', calculate_age(2019, 1819))
python
# 返回一个布尔值
def is_even (n):
  if n % 2 == 0:
    print('even')
    return True    # return stops further execution of the function, similar to break 
  return False
print(is_even(10)) # True
print(is_even(7))  # False
python
# 返回一个列表
def find_even_numbers(n):
  evens = []
  for i in range(n + 1):
    if i % 2 == 0:
      evens.append(i)
  return evens
print(find_even_numbers(10))

带默认参数的函数 ​

python
# 将默认值传递给参数,如果不传递参数,则将使用它们的默认值
def greetings (name = 'Peter'):
  message = name + ', welcome to Python for Everyone!'
  return message
print(greetings())
print(greetings('he'))

def generate_full_name (first_name = 'he', last_name = 'fang'):
  space = ' '
  full_name = first_name + space + last_name
  return full_name

print(generate_full_name())
print(generate_full_name('David','Smith'))

def calculate_age (birth_year,current_year = 2021):
  age = current_year - birth_year
  return age
print('Age: ', calculate_age(1821))

def weight_of_object (mass, gravity = 9.81):
  weight = str(mass * gravity)+ ' N' # the value has to be changed to string first
  return weight
print('Weight of an object in Newtons: ', weight_of_object(100)) # 9.81 - average gravity on Earth's surface
print('Weight of an object in Newtons: ', weight_of_object(100, 1.62)) # gravity on the surface of the Moon

任意数量的参数 ​

python
# 不知道传递给函数的参数的数量
# 通过在参数名前添加 * 来创建一个可以接受任意数量参数的函数
def sum_all_nums(*nums):
  total = 0
  for num in nums:
    total += num     # same as total = total + num 
  return total
print(sum_all_nums(2, 3, 5)) # 10

默认参数和任意数量的参数 ​

python
def generate_groups (team,*args):
  print(team)
  for i in args:
    print(i)
print(generate_groups('Team-1','he','Brook','David','fang'))

函数作为参数 ​

python
#You can pass functions around as parameters
def square_number (n):
  return n * n
def do_something(f, x):
  return f(x)
print(do_something(square_number, 3)) # 27

装饰器 ​

python
# Normal function
# 创建装饰函数，我们需要一个带有内部包装函数的外部函数
def greeting():
  return 'Welcome to Python'
def uppercase_decorator(function):
  def wrapper():
    func = function()
    make_uppercase = func.upper()
    return make_uppercase
  return wrapper
g = uppercase_decorator(greeting)
print(g())          # WELCOME TO PYTHON

## Let us implement the example above with a decorator

'''This decorator function is a higher order function
that takes a function as a parameter'''
def uppercase_decorator(function):
  def wrapper():
    func = function()
    make_uppercase = func.upper()
    return make_uppercase
  return wrapper
@uppercase_decorator
def greeting():
  return 'Welcome to Python'
print(greeting())   # WELCOME TO PYTHON
python
# 将多个装饰器应用于单个函数

'''These decorator functions are higher order functions
that take functions as parameters'''

# First Decorator
def uppercase_decorator(function):
  def wrapper():
    func = function()
    make_uppercase = func.upper()
    return make_uppercase
  return wrapper

# Second decorator
def split_string_decorator(function):
  def wrapper():
    func = function()
    splitted_string = func.split()
    return splitted_string
  return wrapper

@split_string_decorator
@uppercase_decorator     # order with decorators is important in this case - .upper() function does not work with lists
def greeting():
  return 'Welcome to Python'
print(greeting())   # WELCOME TO PYTHON
python
# 在装饰器函数中接受参数
def decorator_with_parameters(function):
  def wrapper_accepting_parameters(para1, para2, para3):
    function(para1, para2, para3)
    print("I live in {}".format(para3))
  return wrapper_accepting_parameters

@decorator_with_parameters
def print_full_name(first_name, last_name, country):
  print("I am {} {}. I love to teach.".format(
    first_name, last_name, country))

print_full_name("he", "fang",'Finland')

map ​

INFO

  • 定义
    • 用于将一个函数应用到可迭代对象的每个元素上，并返回一个包含结果的新迭代器
  • 语法
    • map(function, iterable, ...)
      • function: 一个函数对象，定义了如何处理 iterable 中的每个元素。这个函数可以接收一个或多个参数
      • iterable: 一个或多个可迭代对象，例如列表、元组、集合等。map() 会依次将 iterable 中的元素作为参数传递给 function
python
numbers = [1, 2, 3, 4, 5] # iterable
def square(x):
  return x ** 2
numbers_squared = map(square, numbers)
print(list(numbers_squared))    # [1, 4, 9, 16, 25]
# Lets apply it with a lambda function
numbers_squared = map(lambda x : x ** 2, numbers)
print(list(numbers_squared))    # [1, 4, 9, 16, 25]
python
numbers_str = ['1', '2', '3', '4', '5']  # iterable
numbers_int = map(int, numbers_str)
print(list(numbers_int))    # [1, 2, 3, 4, 5]
python
names = ['he', 'fang']  # iterable
def change_to_upper(name):
  return name.upper()

names_upper_cased = map(change_to_upper, names)
print(list(names_upper_cased))    # ['he', 'fang']

# Let us apply it with a lambda function
names_upper_cased = map(lambda name: name.upper(), names)
print(list(names_upper_cased))    # ['he', 'fang']

filter ​

INFO

  • 定义
    • 用于根据特定条件从可迭代对象中筛选出符合条件的元素
  • 语法：
    • filter(function, iterable)
      • function: 一个布尔函数，用于测试可迭代对象中的每个元素
      • 函数应返回 True 或 False。如果 function 为 None，则会将 iterable 中的所有 True 值返回
      • iterable: 一个可迭代对象，如列表、元组、集合等
python
# Lets filter only even numbers
numbers = [1, 2, 3, 4, 5]  # iterable
def is_even(num):
  if num % 2 == 0:
    return True
  return False
even_numbers = filter(is_even, numbers)
print(list(even_numbers))       # [2, 4]
python
# Lets filter only odd numbers
numbers = [1, 2, 3, 4, 5]  # iterable
def is_odd(num):
  if num % 2 != 0:
    return True
  return False
odd_numbers = filter(is_odd, numbers)
print(list(odd_numbers))       # [1, 3, 5]
python
# Filter long name
names = ['he', 'fang']  # iterable
def is_name_long(name):
  if len(name) > 3:
    return True
  return False
long_names = filter(is_name_long, names)
print(list(long_names))         # ['fang']

reduce ​

INFO

  • 定义
    • 用于对一个序列进行累计操作
  • 语法
    • from functools import reduce
    • reduce(function, iterable[, initializer])
      • function: 一个二元函数，用于将序列的前两个元素进行计算，随后将计算结果与下一个元素进行计算，依此类推
      • iterable: 一个可迭代对象，如列表、元组等
      • initializer (可选): 初始值。如果提供了初始值，则它会在第一个元素之前被计算
python
numbers_str = ['1', '2', '3', '4', '5']  # iterable
def add_two_nums(x, y):
  return int(x) + int(y)
total = reduce(add_two_nums, numbers_str)
print(total)    # 15

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