Python简明语法

0.前言

本篇文章参考了python3-in-one-pic。

这篇文章的主要目的是希望大家在看完之后能够对python的主体知识有个大致的了解,而且每个基础知识都有一定的例子做支撑，能够更容易理解记忆。主体内容都是从上述网址中搬移过来的，前期主要做了一些翻译工作，后期会对里面的语句进行详细解析。

1.语法规则（Syntax Roles）

1.1 区分大小写（Case-sensitive）

a = 1
A = 2
print(a is not A)	# True

1.2 注释（Comments）

# 注释会被忽略（Comments will be ignored）

1.3 代码块由首行缩进界定（Code blocks are defined by their indentation）

每一个首行缩进使用4个空格（Use 4 spaces per indentation）

2.基本数据类型（Native Datatypes）

2.1 数字（Number）

2.1.1 整型（integer）

a = 1
b = 0x10        # 16
print(type(a))  # <class 'int'>

2.1.2 浮点型（float）

C = 1.2
d = .5          # 0.5
g = .314e1      # 3.14
print(type(g))  # <class 'float'>

2.1.3 复数（complex）

e = 1 + 2j 
f = complex(1, 2)
print(type(e))		# <class 'complex'>
print(f == e)		# True

2.1.4 操作符（Operators）

## Operators:+-*/**//%
print(1 + 1)		# 2
print(2 - 2)		# 0
print(3 * 3)		# 9
print(5 / 4)		# 1.25
print(2 ** 10)		# 1024
print(5 // 4)		# 1
print(5 % 4)		# 1

2.1.5 类型转换（Casting）

# Integer/String -> Float
print(float.__doc__)
"""
float(x)->floating point number
Convert a string or number to a floating point number, if possible.
"""
print(float(3))         # 3.0
print(3 / 1)            # 3.0
print(float("3.14"))    # 3.14
# Float/String -> Integer
print(int.__doc__)
"""
int(x=0)->integer 
int(x,base=10)->integer
...
"""
print(int(3.14))                # 3
print(int("3",base = 10))       # 3
print(int("1010",base = 2))     # 10
print(int("0b1010",base = 8))	# 10

2.2 字符串（String）

s1 = ':dog:\n'
s2 = "Dogge's home"
s3 = """
Hel1o,
Dogge!
"""
print(type(s1))				# <class 'str'>
print("%s,%s,%s"%(s1,s2,s3))
# :dog:
# , Dogge's home,
# Hello,
# Dogge!

2.2.1 长度（Length）

print(len(s1))	# 6

2.2.2 分片（Slicing）

s = 'study and practice'
print('{0}:{1}'.format(s[:5], s[-8:]))	# study:practice

2.2.3 操作符（Opetator）

print("abc" + "." + "xyz")	# "abc.xyz"

2.2.4 类型转换（Casting）

print(str.__doc__)
"""
strCobject='') -> str 
str(bytes_or_buffer[, encoding[, errors]) -> str
"""
print(str(3.14))		# "3.14"
print(str(3))			# "3"
print(str([1,2,3]))		# "[1,2,3]"
print(str((1,2,3)))		# "(1,2,3)"
print(str({1,2,3}))		# "{1,2,3}"
print(str({'python': '*.py', 'javascript': '*.js'}))
"{'python': '*.py', 'javascript': '*.js'}"

2.3 字节（Byte）

2.3.1 list of ascii character

2.3.2 0-255/x00-xff

byt = b'abc'
print(type(byt))		# <class 'bytes'>
print(byt[0] == 'a')	# False
print(byt[0] == 97)		# True

2.3.3 Length

print(len(byt))			# 3

2.4 布尔值（Boolean）

True
False
print(type(True))		# <class 'bool'>

2.5 空类型（None）

print(None is None)		# True
print(type(None))		# <class 'NoneType'>

2.6 列表（List）

l = ['python', 3, 'in', 'one']
print(type(l))			# <class 'list'>

2.6.1 长度（Length）

print(len(l))			# 4

2.6.2 分片（Slicing）

print(1[0])             # 'python'
print(1[-1])            # 'one'
print(1[1:-1])          # [3, 'in']

2.6.3 更改（Alter）

l.append(' pic')		# None
# l == ['python', 3, 'in', 'one', 'pic']
l.insert(2,'.4.1')		# None
# l == ['python', 3, '.4.1', 'in', 'one', 'pic']
l.extend([!',!'])
# l == ['python', 3, '.4.1', 'in', 'one', 'pic', '!', '!']
print(1. pop())			# '!'
# l == ['python', 3, '.4.1', 'in', 'one', 'pic', '!']
print(1. pop(2))		# '.4.1'
# l == ['python', 3, 'in', 'one', 'pic', '!']
l.remove("in")
# l == ['python', 3, 'one', 'pic', '!']
del l[2]
# l == ['python', 3, 'pic', '!']

2.6.4 索引（Index）

print(l.index('pic'))	# 2

2.7 元组（Tuple）

不可更改的列表（Immutable list）

tp=(1,2,3,[4,5])
print(type(tp))			# <class 'tuple'>

## Length 
print(len(tp))			# 4
print(tp[2])			# 3
tp[3][1]=6
print(tp)				# (1, 2, 3, [4, 6])

## Single element 
tp=(1,)					# Not tp = (1)

分配多个变量值（assign multiple values）

v = (3, 2, 'a')
(c, b, a) = v 
print(a, b, c)			# a 2 3

2.8 集合（Set）

st = {'s','e','T'}
print(type(st))			# <class 'set'>

##Length 
print(ien(st))			# 3
##Empty 
st = set()
print(len(st))			# 0

st = {}
print(type(st))			# <class 'dict'>

	Alter
st = set(['s', 'e', 'T'])
st.add('t')				# st == {'s', 'e', 't', 'T'} 
st.add('t")				# st == {'s', 'e', 't', 'T'}
st.update(['!',!'])
# st == {'s', 'e', 't', 'T', '!'}
st.discard('t')			# st == {'T',!",'s','e'}	# No Error 
st.remove('T')			# st == {'s', 'e', '!'}		# KeyError 
st.pop()				# 's'
# st == {'e'}
st.clear()				# st == set()

2.9 字典（Dict）

dic = {}
print(type(dic))		# <class 'dict'>
dic = {'k1': 'v1', 'k2': 'v2'}

## Length 
print(len(dic))             # 2

print(dic['k2'])            # 'v2'
print(dic.get('k1'))        # 'v1'
print(dic.get('k3','v0'))   # 'vo'

dic['k2'] = 'v3'
print(dic)                  # {'k1': 'v1', 'k2': 'v3'}

print('k2' in dic)          # True 
print('v1' in dic)          # False

3.流程控制（Flow Control）

3.1 如果（If）

import sys 
if sys.version_info. major < 3: 
	print("Version 2.X")
elif sys.version_info. major > 3: 
	print("Future")
else:
	print("Version 3.X")

3.2 循环（Loop）

3.2.1 For

for i in "Hello":
	print(i)

3.2.2 While

prod = 1
i = 1
while i < 10:
	prod = prod * i
	i += 1
print(prod)

3.2.3 break / continue

for n in range(2, 10): 
	if n % 2 == 0:
		print("Found an even number", n)
		continue 
	if n > 5: 
	print("GT 5!")
	break

3.2.4 迭代器 & 生成器（Iterators & Generators）

python = iter("Python"）
print(python）
# <str_iterator object at 0x10293f8d0>
for i in python：
	print（i）
# P
# y
# t
# h
# o
# n

def reverse(data): 
	for index in range(len(data)-1, -1, -1): 
		yield data[index]
nohtyp = reverse("Python")
print(nohtyp)
# <generator object reverse at 9x1829539e8>
for i in nohtyp: 
	print(i)
# n
# o
# h
# t
# y
# P

3.3 解析式（Comprehensions）

3.3.1 列表（List）

s = [2 * x for x in range(10) if x ** 2 > 3]
print(s)
# [4, 6, 8, 10, 12, 14, 16, 18]

pairs = [(x, y)for x in range(2) for y in range(2)]
print(pairs)
# [(0, 0), (0, 1), (1, 0), (1, 1)]

3.3.2 集合（Set）

s = {2 * x for x in range(10) if x ** 2 > 3}
print(s)
# 4, 6, 8, 10, 12, 14, 16, 18}

pairs = set([(x, y)for x in range(2) for y in range(2)])
print(pairs)
# {(0, 1), (1, 0), (e, 0), (1, 1)}

3.3.3 字典（Dict）

ls = {s: len(s) for s in ["Python", "Javascript", "Golang"]}
print(ls)
# {"Python': 6, ' Javascript': 10, ' Golang': 6}

s1 = {v: k for k, v in ls.items)}
print(sl)
# {10: 'Javascript', 6: 'Golang'}

4.函数（Function）

4.1 定义（Definition）

def f():
	"""return 'Hello, World!'"""
	return "Hello, World!"

print(f())          # "Hello, World!"
print(f.__doc__)    # "return 'Hello, World!'"

4.2 参数（Arguments）

4.2.1 默认参数（default arguments）

def f(name = "World"):
	"""return 'Hello, $name'"""
	return "Hello,{}!".format(name)

print(f())              # 'Hello, World!'
print(f("Python"))      # 'Hello, Python!'

4.2.2 关键词参数（keyword arguments）

def f(v,l = "Python"):
	"""return '$v, $l'"""
	return "{}, {}!".format(v, l)

print(f("Hello"))           # "Hello, Python!"
print(f("Bye", "C/C++"))    # "Bye, C/C++!"

4.2.3 任意参数（arbitrary arguments）

def f(*args, con = "&"): 
	print(isinstance(args, tuple)) 
	print("Hello", con.join(args))
f("Python", "C", "C++", con = "/")
# True
# "Hello Python/C/C++"

def f(*args, **kargs): 
	print("args", args)
	print("kargs", kargs)
	print("FP: {} & Scripts: {}".format(kargs.get("fp"), "/".join(args)))
f("Python", "Javascript", ms = "C++", fp = "Haskell")
# args ('Python', 'Javascript')
# kargs {'ms': 'C++', 'fp': 'Haskell'}
# FP: Haskell and Scripts: Python/Javascript

4.2.4 lambda表达式（Lambda）

pairs = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
pairs.sort(key = lambda pair: pair[1])
print(pairs)
"[(4, 'four'), (1, 'one'), (3, 'three'), (2, 'two')]"
pairs.sort(key = lambda pair: pair[0])
print(pairs)
"[(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]"

4.2.5 装饰器（Decorator）

def log(f): 
	def wrapper():
		print("Hey log~")
		f()
		print("Bye log~")
	return wrapper
	@Log 
	def fa(): 
		print("This is fa!")
	# Equal to...
	def fb(): 
		print("This is fb!")
	fb = Log(fb)
	fa()
	print("*"*10)
	fb()
# Hey log～
# This is fa！
# Bye log~
# **********
# Hey log~
# This is fb！
# Bye log~

5.类（面向对象）（Class（OOP））

5.1 类（Class）

class Animal:
	"""This is an Animal."""
	def fly(): 
		print("I can fly!")
a = Animal() 
a.fly()             # I can fly!
print(a.__doc__)    # This is an Animal

5.2 构造函数（init & self）

class Animal:
	"""This is an Animal"""
	def __init__(self, can_fly = False):
	 	print("Calling__init__() when instantiation!")
		self.can_fly = can_fly 
	def fly(self): 
		if self.can_fly: 
			print("I CAN fly!")
		else: 
			print("I can not fly!")
a = Animal()                # Calling __init__() when instantiation!
a.fly()                     # I can not fly!
b = Animal(can_fly = True)  # Calling __init__() when instantiation!
b.fly()                     # I CAN fly!

5.3 实例（Instance）

class Animal: 
	pass 
class Human: 
	pass 
a = Animal()
h = Human()
print(isinstance(a,Animal))	# True 
print(isinstance(h,Animal))	# False

5.4 继承（Inheritance）

class Animal:
	"""This is an Animal"""
	def __init__(self, can_fly = False): 
		self.can_fly = can_fly 
	def fly(self): 
		if self.can_fly: 
			print("I CAN fly!")
		else:
			print("I can not fly!")
class Dog(Animal):
	"""This is a Dog"""
	def bark(self): 
		print("Woof!")
d = Dog() 
d.fly()				# I can not fly!
d.bark()			# Woof!

5.5 重载（Override）

class Animal:
	"""This is an Animal"""
	def __init__(self, can_fly = False): 
		self.can_fly = can_fly 
	def fly(self): 
		if self.can_fly: 
			print("I CAN fly!")
		else: 
			print("I can not fly!")
class Bird:
	"""This is a Bird"""
	def fly(self): 
		printC"I'm flying high!")
bird = Bird()
bird.fly()			# I'm flying high!

6.模块（Module）

6.1 导入（Import）

import os 
print（os.name)
# posix 
from sys import version_info as PY_VERSION 
print("VERSON:{}.{}".format(PY_VERSION.major, PY_VERSION. minor))
# VERSON:3.5
from math import *
print(pi)
# 3.141592653589793

6.2 搜索路径（Search Path）

1.current directory
2.echo $PYTHONPATH
3.sys.path

6.3 打包（Package）

""
MyModule/
|--SubModuleOne/
	|--__init__.py
	|--smo.py
# smo.py 
def run): 
	print("Running MyModule.SubModuleOne. smo!")
"""
from MyModule.SubModule import smo 
smo.run()
# Running MyModule.SubModuleOne.smo!

7.Pythonic

8.标准函数库（Standard Libraries）