中途退出

exit()

使用缩进来标识代码块，而不是使用{}

空格至少有1个。

if 5 > 2:
  print("Five is greater than two!")

多行注释"""

"""
This is a comment
written in
more than just one line
"""
print("Hello, World!")

快速赋值

x, y, z = "Orange", "Banana", "Cherry"

不能直接用+拼接数字和字符串

x = 5
y = "John"
print(x + y)#ERROR

内置数据类型

用e或者E来表示底数10

x = 35e3
y = 12E4
z = -87.7e100

随机数

import random

print(random.randrange(1, 10))#a number in [1,10)

flont转int向下取整

y = int(2.8) # y will be 2

String常用的函数

• strip()去掉字符串首尾空格
• upper(), lower()大小写转换
• replace()替换
• split()分割字符串
• 判断是否包含字串,in，not in,类似Java中的contains()

txt = "The rain in Spain stays mainly in the plain"
x = "ain" in txt
print(x)

• +字符串拼接
• 占位符使用

quantity = 3
itemno = 567
price = 49.95
myorder = "I want {} pieces of item {} for {} dollars."
print(myorder.format(quantity, itemno, price))

• 其他常用函数

​

布尔值

首字母大写
True,False

• 字符串
  不是空串为True,反之为False
• 数字
  0：False,其他：True
• 列表，元组，set，字典
  空集合：False,其他：True

总结，下面的代码均会返回False：

bool(False)
bool(None)
bool(0)
bool("")
bool(())
bool([])
bool({})

Python操作符
** 幂运算

z = x ** y # z = x ^ y

/浮点除法
//结果向下取整

浮点除和整数除

Python不用&&,||和!，而是

python逻辑运算符

其他语言没有的操作符
in,not in

x = ["apple", "banana"]
print("banana" in x)
# returns True because a sequence with the value "banana" is in the list

Python数据结构

• 列表（[]来表示）

thislist = ["apple", "banana", "cherry"]
print(thislist)

列表的增删改查

thislist = ["apple", "banana", "cherry"]
thislist.append("orange")
thislist.insert(1, "orange")
thislist.remove("banana")
thislist.pop()
del thislist[0]
thislist.clear()
del thislist
#复制list
mylist = thislist.copy()
mylist1 = list(thislist)
#合并list
list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]
list3 = list1 + list2
print(list3)

构造函数，注意((,))

thislist = list(("apple", "banana", "cherry")) # note the double round-brackets
print(thislist)

常用API

list api

• 元组（ 用()来表示）
  unchangeable

thistuple = ("apple", "banana", "cherry")
print(len(thistuple))

如果只要有一个元素，注意逗号

thistuple = ("apple",)
print(type(thistuple))#tuple

thistuple = ("apple")
print(type(thistuple))#str

tuple()构造函数

thistuple = tuple(("apple", "banana", "cherry")) # note the double round-brackets
print(thistuple)

• set
  unordered,unindexed,无序的，定义之后，无法确定它的顺序，所以不能通过下标的方式进行访问。
  set的增删改查

thisset = {"apple", "banana", "cherry"}
thisset.add("orange")#添加单个元素
thisset.update(["orange", "mango", "grapes"])#添加过个元素
#If the item to remove does not exist, discard() ,remove() will NOT raise an error.
thisset.discard("banana")
thisset.remove("banana")
#两个set进行union
set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}
set3 = set1.union(set2)
print(set3)

使用update()合并

set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}
set1.update(set2)
print(set1)

set()构造函数

thisset = set(("apple", "banana", "cherry")) # 注意是双括号
print(thisset)

• 字典Dictionary

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict)
x = thisdict.get("model")
thisdict["year"] = 2018
#遍历key
for x in thisdict:
  print(x)
#遍历value
for x in thisdict.values():
  print(x)
#同时遍历key和value
for x, y in thisdict.items():
  print(x, y)
#删除
del thisdict["model"]

dict()构造函数

thisdict = dict(brand="Ford", model="Mustang", year=1964)

• if else语句
  elif

a = 33
b = 33
if b > a:
  print("b is greater than a")
elif a == b:
  print("a and b are equal")

pass(什么都不做，作为占位符)

a = 33
b = 200

if b > a:
  pass

• 函数
  def

def my_function():
  print("Hello from a function")

my_function()

变长参数的函数

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

my_function("Emil", "Tobias", "Linus")

带默认值的函数

def my_function(country = "Norway"):
  print("I am from " + country)

my_function("Sweden")
my_function("India")
my_function()
my_function("Brazil")

• Python Lambda
  lambda函数指的是一个小的匿名函数。

#可以有多个参数，但是只能有一个语句
lambda 参数: 语句
# 语句会被执行，然后返回结果

例如：

x = lambda a, b : a * b
print(x(5, 6))

• 类和对象

class MyClass:
  x = 5

p1 = MyClass()
print(p1.x)

__init__()函数
每个类都有__init__()，初始化函数，（类似Java的构造函数）

class Person:
  def __init__(self, name, age):
# self类似Java的this指针，指向当前对象。
    self.name = name
    self.age = age

p1 = Person("John", 36)

print(p1.name)
print(p1.age)

对象中添加方法：

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

  def myfunc(self):
    print("Hello my name is " + self.name)

p1 = Person("John", 36)
p1.myfunc()

• 继承
  父类：

class Person:
  def __init__(self, fname, lname):
    self.firstname = fname
    self.lastname = lname

  def printname(self):
    print(self.firstname, self.lastname)

子类：

class Student(Person):
  pass

调用父类的构造函数

class Student(Person):
  def __init__(self, fname, lname):
    super().__init__(fname, lname)#super()
    self.graduationyear = 2019#子类添加graduationyear 域

  def welcome(self):#子类添加方法，同名可以override父类方法。
      print("Welcome", self.firstname, self.lastname, "to the class of", self.graduationyear)

• 迭代器
  python的列表、set和字典都是可以迭代的，iter()返回一个迭代器。

mytuple = ("apple", "banana", "cherry")
myit = iter(mytuple)

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

• Module模块
  module和库函数类似

创建:

#将代码保存为.py文件
#mymodule.py
def greeting(name):
  print("Hello, " + name)

使用：

import mymodule
mymodule.greeting("Jonathan")

重命名模块

import mymodule as mx

python自带