python快速入门 数据输出和基本类型 常用的循环遍历等

print("hello world")

var=None
print(var) #None
if True:
var=100

print(var) #100

# 关键字
# and  ==  C++ &&
# del  ==  C++ delete
# from ???
# not  ==  C++ !
# while
# as   ???
# elif == else if
# global ??? 标记全局变量
# or  ==  C++ ||
# with ??? 跟as一起用
# assert 断言
# else
# if
# pass 空语句
# yield  生成器和迭代器
# break
# except 相当与 C++ catch
# import 相当与 #include
# print
# class
# exec
# in 判断一个对象是不是属于一个集合
# raise 相当于C++的throw
# continue
# finally
# is 判断两个对象是不是同一个对象
# return
# def 定义函数
# for
# lambda 匿名函数
# try

# 标识符
# python标识符定义和C++要求是一样的

# 操作符
#

# 代码结构
a = 10 # 一句代码
b = 20
c = 30  # 代码块
d = 40

# 同一代码块的代码应该有相同缩进

# 条件判断
if a == b:
    print("a equal b")
    print("aaaa")
else:
    print(" a not equal b")

if c == d:
    pass

if a == b:
    pass
elif c == d:
    pass
else:
    pass

for i in [1, 2, 3, 4]:
    pass

while d < 100:
    d += 1

def funname():
    pass

with as

a = 10912318312831283128312831823812381238123812831283182318238123813
a = 2 ** 256 #2的 256次方
print(a)
print(a)
a = 10.1
a = "hello world"

# number
# bool
a = True
a = False
# string
a = "hell'''o world"
a = 'hell"""o world'
a = '''hello world'''
a = """hello world"""

a = """
hello 
world
"""
#上面这个a[0]会是"" a[1]才是h
a = "hello world"
#a[0]=h
a = "Hello world"
#a[0] = "H" # xxxxxx
# 集合
# 列表
a = [1, 2, 3, 4]
a = [1, "hello", True, 100.1]
a[0] = 100
a.append(100)
print(a)

# 元组:不可修改
a = (1, 2, 3, 4)
a = (1, "hello", True, 100.1)
for value in a:
    print(value)

# 字典：key不一定是字符串，key必须是不可改变的
a = {"key":1,
     "key2":2}

a["key3"] = 3
a[100] = 100
a[(1, 2, 3)] = 10

print("..............")
for key in a:
    print(key)
print("..............")

print(a["key2"])

# 集合
a = set([2, 3, 4, 2, 2, 2, 2])
print(a)

字典遍历

a = {"key":1,
"key2":2}

a["key3"] = 3
a[100] = 100
a[(1, 2, 3)] = 10

print("..............")
for key in a:
print(key,a[key])
print("..............")
"""
key 1
key2 2
key3 3
100 100
(1, 2, 3) 10
"""

列表遍历

#!/usr/bin/env python
# -*- coding: utf-8 -*-
if __name__ == '__main__':
    list = ['html', 'js', 'css', 'python']

    # 方法1
    print '遍历列表方法1：'
    for i in list:
        print ("序号：%s   值：%s" % (list.index(i) + 1, i))

    print '\n遍历列表方法2：'
    # 方法2
    for i in range(len(list)):
        print ("序号：%s   值：%s" % (i + 1, list[i]))

    # 方法3
    print '\n遍历列表方法3：'
    for i, val in enumerate(list):
        print ("序号：%s   值：%s" % (i + 1, val))

    # 方法3
    print '\n遍历列表方法3 （设置遍历开始初始位置，只改变了起始序号）：'
    for i, val in enumerate(list, 2):
        print ("序号：%s   值：%s" % (i + 1, val))