分支结构

1.if-else

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a = 200
b = 66
print("A") if a > b else print("=") if a == b else print("B")

x = 1
y = 2
if x == y:
  print("a = b")
elif x > y:
  print("a > b")
else:
  pass

2.while

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x = 4
while x > 0:
  print(x)
  x -= 1
  if x == 2:
    break
  elif x == 1:
    continue

3.for

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for x in "bananas":
  print(x)

for x in range(3,50,6):
  print(x)

函数

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#初始化赋值
def add(x = 0 , y = 0):
  print(x + y)

add(x,y)

#传参时赋值
def my_function(child3, child2, child1):
  print("The youngest child is " + child3)

my_function(child1 = "Phoebe", child2 = "Jennifer", child3 = "Rory")

#未知参数
def my_function(*kids):
  print("The youngest child is " + kids[2])

my_function("Phoebe", "Jennifer", "Rory")

#lambda 匿名函数
def myfunc(n):
  return lambda a : a * n
mytripler = myfunc(3) #返回值是一个函数
print(mytripler(11))

数组

类 and 对象

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class Person:
  def __init__(self, name, age):
    self.name = name
    self.age = age

  def myfunc(self):#self也可以是其他名字，总之，代表一个指向自己的参数
    print("Hello my name is " + self.name)

p1 = Person("Bill", 63)
p1.myfunc()

del p1
del Person

继承

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#create
class Student(Person):
  def __init__(self, fname, lname):
    Person.__init__(self, fname, lname)

#super()函数自动调用父类的方法
class Student(Person):
  def __init__(self, fname, lname):
    super().__init__(fname, lname)

迭代器

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#有迭代方法的对象使用了该方法，创建了一个迭代器的对象
mystr = "banana"
myit = iter(mystr)

print(next(myit))
print(next(myit))
print(next(myit))

mystr = "banana"
for x in mystr:
  print(x)
#实际上也是创建了一个迭代器

#给类写迭代器方法
class MyNumbers:
  def __iter__(self):
    self.a = 1
    return self

  def __next__(self):
    if self.a <= 20:
      x = self.a
      self.a += 1
      return x
    else:
      raise StopIteration #终止迭代

myclass = MyNumbers()
myiter = iter(myclass)

for x in myiter:
  print(x)

模块

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import func as my_func
my_func.add(1,2)
#假设func.py中含有add函数

#导入
def greeting(name):
  print("Hello, " + name)

person1 = {
  "name": "Bill",
  "age": 63,
  "country": "USA"
}
 #then
from mymodule import person1
print (person1["age"])#此时就只是person1了，不用mymodule.person1

调试

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try:
  f = open("demofile.txt")
  f.write("Lorum Ipsum")
except:
  print("Something went wrong when writing to the file")
else:
    print("fine")
finally:
  f.close()

#引发异常
x = -1

if x < 0:
  raise Exception("Sorry, no numbers below zero")

input输入

format

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quantity = 3
itemno = 567
price = 52
myorder = "I want {0} pieces of item number {1} for {2:.2f} dollars." #添加索引 格式化输入
print(myorder.format(quantity, itemno, price))

myorder = "I have a {carname}, it is a {model}."#如果在占位符中添加名称索引，名称必须在format中被初始化
print(myorder.format(carname = "Porsche", model = "911"))