Python基础

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

类型	标识
Text Type:	str
Numeric Types:	int, float, complex
Sequence Types:	list, tuple, range
Mapping Type:	dict
Set Types:	set, frozenset
Boolean Type:	bool
Binary Types:	bytes, bytearray, memoryview

Example	Data Type
x = "Hello World"	str
x = 20	int
x = 20.5	float
x = 1j	complex
x = ["apple", "banana", "cherry"]	list
x = ("apple", "banana", "cherry")	tuple
x = range(6)	range
x = {"name" : "John", "age" : 36}	dict
x = {"apple", "banana", "cherry"}	set
x = frozenset({"apple", "banana", "cherry"})	frozenset
x = ==True==	bool
x = b"Hello"	bytes
x = bytearray(5)	bytearray
x = memoryview(bytes(5))	memoryview

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

Method	Description
capitalize()	Converts the first character to upper case
casefold()	Converts string into lower case
center()	Returns a centered string
count()	Returns the number of times a specified value occurs in a string
encode()	Returns an encoded version of the string
endswith()	Returns true if the string ends with the specified value
expandtabs()	Sets the tab size of the string
find()	Searches the string for a specified value and returns the position of where it was found
format()	Formats specified values in a string
format_map()	Formats specified values in a string
index()	Searches the string for a specified value and returns the position of where it was found
isalnum()	Returns True if all characters in the string are alphanumeric
isalpha()	Returns True if all characters in the string are in the alphabet
isdecimal()	Returns True if all characters in the string are decimals
isdigit()	Returns True if all characters in the string are digits
isidentifier()	Returns True if the string is an identifier
islower()	Returns True if all characters in the string are lower case
isnumeric()	Returns True if all characters in the string are numeric
isprintable()	Returns True if all characters in the string are printable
isspace()	Returns True if all characters in the string are whitespaces
istitle()	Returns True if the string follows the rules of a title
isupper()	Returns True if all characters in the string are upper case
join()	Joins the elements of an iterable to the end of the string
ljust()	Returns a left justified version of the string
lower()	Converts a string into lower case
lstrip()	Returns a left trim version of the string
maketrans()	Returns a translation table to be used in translations
partition()	Returns a tuple where the string is parted into three parts
replace()	Returns a string where a specified value is replaced with a specified value
rfind()	Searches the string for a specified value and returns the last position of where it was found
rindex()	Searches the string for a specified value and returns the last position of where it was found
rjust()	Returns a right justified version of the string
rpartition()	Returns a tuple where the string is parted into three parts
rsplit()	Splits the string at the specified separator, and returns a list
rstrip()	Returns a right trim version of the string
split()	Splits the string at the specified separator, and returns a list
splitlines()	Splits the string at line breaks and returns a list
startswith()	Returns true if the string starts with the specified value
strip()	Returns a trimmed version of the string
swapcase()	Swaps cases, lower case becomes upper case and vice versa
title()	Converts the first character of each word to upper case
translate()	Returns a translated string
upper()	Converts a string into upper case
zfill()	Fills the string with a specified number of 0 values at the beginning

​

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