python 基础

if <条件判断1>:
   <执行1>
elif <条件判断2>:
   <执行2>
elif <条件判断3>:
   <执行3>
else:
   <执行4>

sum = 0
for x in range(101):
   sum = sum + x
print(sum)

def my_abs(x):
   if not isinstance(x, (int, float)):
       raise TypeError('bad operand type')
   if x >= 0:
       return x
   else:
       return -x

def calc(*numbers):
   sum = 0
   for n in numbers:
       sum = sum + n * n
   return sum

# 汉诺塔递归
def hano(a,b,c,n):
   if n==1:
       print(a,'->',c) # 当只剩下一个盘子时，直接从源柱搬到目标柱
   else:
       hano(a,c,b,n-1) # 否则将源柱的n-1个盘子借助源柱搬到中柱
       print(a,'->',c) # 再将源柱最后一个盘子直接搬到目标柱
       hano(b,a,c,n-1) # 将中柱的n-1个盘子借助源柱搬到目标柱
   return
hano('A','B','C',10)

l=list(range(100))
for n in l:
   print(n)

>>> from collections import Iterable
>>> isinstance('abc', Iterable) # str是否可迭代
True
>>> isinstance([1,2,3], Iterable) # list是否可迭代
True
>>> isinstance(123, Iterable) # 整数是否可迭代
False

import os
a = [d for d in os.listdir('.')]
print(a)

g = (x * x for x in range(10))
print(next(g))
for n in g:
    print(n)

reduce(f, [x1, x2, x3, x4]) = f(f(f(x1, x2), x3), x4)
b=list(map(str, [1, 2, 3, 4, 5, 6, 7, 8, 9])) # str() 将参数转成字符串
print(b)

# 将str 转 int 函数（使用 dict, map, reduce）
from functools import reduce
DIGITS = {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9}
def str2int(s):
   def fn(x, y):
       return x * 10 + y
   def char2num(s):
       return DIGITS[s]
   return reduce(fn, map(char2num, s))
filter() 筛选器
def is_odd(n):
   return n % 2 == 1

list(filter(is_odd, [1, 2, 4, 5, 6, 9, 10, 15]))
sorted 排序
sorted([36, 5, -12, 9, -21], key=abs)
sorted(['bob', 'about', 'Zoo', 'Credit'], key=str.lower, reverse=True)
返回函数
def lazy_sum(*args):
   def sum():
       ax = 0
       for n in args:
           ax = ax + n
       return ax
   return sum

>>> f = lazy_sum(1, 3, 5, 7, 9)
>>> f
<function lazy_sum.<locals>.sum at 0x101c6ed90>

>>> f()
25

lambda args : expresion
list(map(lambda x: x * x, [1, 2, 3, 4, 5, 6, 7, 8, 9]))
f = lambda x: x * x

def log(func):
   def wrapper(*args, **kw):
       print('call %s():' % func.__name__)
       return func(*args, **kw)
   return wrapper

@log
def now():
   print('2015-3-25')

>>> now()
call now():
2015-3-25

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

' a test module '

__author__ = 'Michael Liao'

import sys

def test():
   args = sys.argv
   if len(args)==1:
       print('Hello, world!')
   elif len(args)==2:
       print('Hello, %s!' % args[1])
   else:
       print('Too many arguments!')

if __name__=='__main__':
   test()]

if __name__=='__main__':
   test()

def _private_1(name):
    return 'Hello, %s' % name

def _private_2(name):
    return 'Hi, %s' % name

def greeting(name):
    if len(name) > 3:
        return _private_1(name)
    else:
        return _private_2(name)

class Student(object):

    def __init__(self, name, score):
        self.name = name
        self.score = score

    def print_score(self):
        print('%s: %s' % (self.name, self.score))
----------------------------------------------------
s1 = Student('Mike', 90)
s1.print()

class Student(object):

    def __init__(self, name, score):
        self.__name = name
        self.__score = score

    def print_score(self):
        print('%s: %s' % (self.__name, self.__score))

class Man(object):
    def __init__(self):
        pass
    def print(self):
        print('Man')

class Student(Man):
    def __init__(self, name, age):
        self.__name = name
        self.__age = age
    def print(self):
        print('name is %s, age is %s.' %(self.__name, self.__age))

def test():
    print('test')

m = Man()
s1 = Student('Make',12)
s1.score = 90
s1.print()
m.print()

a=123
print(type(a) == int)

class Man(object):
    def __init__(self):
        pass
    def print(self):
        print('Man')
m = Man()
print(type(m) == Man)

print(type(abs))

import types
print(type(abs) == types.FunctionType) # 判断是否是函数类型
isinstance() 判断某一实例是否是某一类型（基本类型、引用类型）
isinstance('123', str)
import types
isinstance(abs, types.BuiltinFunctionType)
isinstance(m, Man)
isinstance([1,2,3], (list, tuple))

l = dir('123')
for i in l:
    print(i)

class Man(object):
    place = 'beijing'
    def __init__(self):
        pass
    def print(self):
        print('Man')
class Student(Man):
    def __init__(self, name, age):
        self.__name = name
        self.__age = age
    def print(self):
        print('name is %s, age is %s.' %(self.__name, self.__age))
s = Student('hh', 12)
print(s.place)

class Animal(object):
    __slots__ = ('name', 'age')
    def __init__(self):
        print('Animal!')
        
class Dog(Animal):
    __slots__ = ()
    def __init__(self):
        print('Dog!')
        
a = Animal()
a.name = 'aa'
a.age = 'bb'
d = Dog()
d.name = 'beijing'

# 不使用@property
class Student(object):
    def __init__(self):
        self.__name = 'abc'
        self.__score = 0

    def name1(self):
        return self.__name

s = Student()
print(s.name1())

# 使用@property
class Student(object):
    def __init__(self):
        self.__name = 'abc'
        self.__score = 0
    @property
    def name1(self):
        return self.__name

s = Student()
print(s.name1) # 在名为name1的get方法定义时加上@property，就可以当成属性来用，一般该方法名与类内部属性名相同

class Student(object):
    def __init__(self):
        self.__name = 'abc'
        self.__score = 0
    @property
    def name(self):
        return self.__name
    @name.setter
    def name(self, value):
        if isinstance(value, str):
            self.__name = value
        else:
            print('cannot set value!')
            return None

s = Student()
print(s.name)
s.name = 111 # 此处自动调用set方法
print(s.name)

# 捕获异常
# err_logging.py

import logging

def foo(s):
    return 10 / int(s)

def bar(s):
    return foo(s) * 2

def main():
    try:
        bar('0')
    except Exception as e:
        logging.exception(e)

main()
print('END')

# 自定义异常类型
# err_raise.py
class FooError(ValueError):
    pass

def foo(s):
    n = int(s)
    if n==0:
        raise FooError('invalid value: %s' % s)
    return 10 / n

foo('0')

# 捕获异常，再次抛出异常
# err_reraise.py

def foo(s):
    n = int(s)
    if n==0:
        raise ValueError('invalid value: %s' % s)
    return 10 / n

def bar():
    try:
        foo('0')
    except ValueError as e:
        print('ValueError!')
        raise

bar()

# 文本文件读取，默认utf-8编码
try:
    f = open('/path/to/file', 'r')
    print(f.read())
finally:
    if f:
        f.close()

# 读取其它其他编码的文本
>>> f = open('/Users/michael/gbk.txt', 'r', encoding='gbk')
>>> f.read()
'测试'

# 二进制读取
>>> f = open('/Users/michael/test.jpg', 'rb')
>>> f.read()
b'\xff\xd8\xff\xe1\x00\x18Exif\x00\x00...' # 十六进制表示的字节

>>> from io import StringIO
>>> f = StringIO()
>>> f.write('hello')
5
>>> f.write(' ')
1
>>> f.write('world!')
6
>>> print(f.getvalue())
hello world!

>>> from io import StringIO
>>> f = StringIO('Hello!\nHi!\nGoodbye!')
>>> while True:
...     s = f.readline()
...     if s == '':
...         break
...     print(s.strip())
...
Hello!
Hi!
Goodbye!

>>> from io import BytesIO
>>> f = BytesIO()
>>> f.write('中文'.encode('utf-8'))
6
>>> print(f.getvalue())
b'\xe4\xb8\xad\xe6\x96\x87'

>>> from io import BytesIO
>>> f = BytesIO(b'\xe4\xb8\xad\xe6\x96\x87')
>>> f.read()
b'\xe4\xb8\xad\xe6\x96\x87'

def student2dict(std):
return {
'name': std.name,
'age': std.age,
'score': std.score
}

>>> print(json.dumps(s, default=student2dict))
{"age": 20, "name": "Bob", "score": 88}

import time
time.strftime('%Y%m%d-%H-%M', time.localtime())  # '20190916-15-27'
time.strftime('%Y%m%d-%H:%M', time.gmtime())  # '20190916-07:27' UTC

>>> import datetime
>>> datetime.datetime.now()
datetime.datetime(2009, 1, 6, 15, 8, 24, 78915)