Python_异常和模块

摘要：例如等价于到结束，但不包括。例如返回没有每次跳跃的间距，默认为。

单个异常处理：

try:
    print(num)

except NameError:
    print("没有定义变量")

except FileNotFoundError:
    print("找不到文件路径")

print(1)

多个异常处理：

try:
    print(num)
    # 11/0
    # open("xxx.txt")
except (NameError, FileNotFoundError, ZeroDivisionError): # 多个异常统一处理
    print("异常")

print(1)

所有异常处理：

try:
    print(num)
except Exception: # 所有异常处理
    print("所有异常处理")

print(1)

查看原来异常输出:

try:
    print(num)
except Exception as err:
    print(err)
print(1)    

没有异常执行

try:
    a = 1

execpt Exception as err:
    print(err)

else:
    print("没有异常执行")

finally:
    print("不管是否出现异常, 都执行")

print(1)     

import time
try:
    f = open("test.txt")
    try:
        while True
            content = f.readline()
            if len(content) == 0:
                break
            time.sleep(2)
            print(content)
    except Exception:
        # pass
        print("文件产生异常")
    finally:
        f.close()
        print("关闭文件")
except Exception:
    print("没有这个文件")

try与except需要同时存在
当函数嵌套的时候，如果函数出现异常，会返回异常，然后捕获到异常

raise: 抛出一个自定义异常

raise语句如果不带参数，就会把当前错误原样抛出。

def main ():
    try:
        s = input("请输入-->")
        if len(s) < 3:
            raise ShortInputException(len(s), 3)
        else:
            print(s)
    except ShortInputException as result:
        print("ShortInputException: 输入的长度是 %d, 长度至少需要是 %d" % (result.length, result.atleast))
    else:
        print("没有异常发生.")

class ShortInputException(Exception):
    """自定义异常类"""
    def __init__(self, length, atleast):
        # super().__init()
        self.length = length
        self.atleast = atleast

main()

如何获取当前模块的文件名: __file__

引入模块

import sys导入模块中的全部功能
from argv import sys, from argv import sys,executable导入模块中的多带带功能
from sys import *
from sys as s 别名

__name__: 用于表示当前模块的名字，同时还能反映一个包的结构

导入输出的是当前模块名

模块被直接运行时模块名为：__main__

if __name__ == "__main__": # 如果模块是被直接运行的，则代码块被运行，如果模块是被导入的，则代码块不被运行。
    # code

常用内建模块

hashlib

import hashlib
m = hashlib.md5()   # 创建hash对象，md5:(message-Digest Algorithm 5)消息摘要算法,得出一个128位的密文
print m             # 
m.update("alogy")  # 更新哈希对象以字符串参数
print m.hexdigest() # 返回十六进制数字字符串

例子：用于注册、登录

import hashlib
import datetime
KEY_VALUE = "alogy"
now = datetime.datetime.now()
m = hashlib.md5()
str = "%s%s" % (KEY_VALUE,now.strftime("%Y%m%d"))
m.update(str.encode("utf-8"))
value = m.hexdigest()
print(value) # c69c59b58209a94f40e6a7a425f9a977

functools

["WRAPPER_ASSIGNMENTS", "WRAPPER_UPDATES", "__builtins__", "__doc__", "__file__", "__name__", "__package__", "cmp_to_key", "partial", "reduce", "total_ordering", "update_wrapper", "wraps"]

partial()

把一个函数的某些参数设置默认值，返回一个新函数，调用这个新函数会更简单。

import functools

def showarg(*args, **kw):
    print(args)
    print(kw)

p1 = functools.partial(showarg, 1, 2, 3)
p1()
p1(4,5,6)
p1(a="python", b="alogy")

p2 = functools.partial(showarg, a=3, b="linux")
p2()
p2(1, 2)
p2(a="python", b="alogy")

wraps()

使用装饰器时，被装饰后等函数其实已经是另外一个函数（函数名等函数属性会发生变化）

添加后由于函数名和函数的doc发生了改变，对测试结果有一些影响，例如:

def note(func):
    "note function"
    def wrapper():
        "wrapper function"
        print("note something")
        return func()
    return wrapper

@note
def test():
    "test function"
    print("I am test")

test()
print(test.__doc__)

运行结果

note something
I am test
wrapper function

所以，Python的functools包中提供了一个叫wraps的装饰器来消除这样的副作用。例如：

import functools
def note(func):
    "note function"
    @functools.wraps(func) # 保存外边函数名
    def wrapper():
        "wrapper function"
        print("note something")
        return func()
    return wrapper

@note
def test():
    "test function"
    print("I am test")

test()
print(test.__doc__)

运行结果

note something
I am test
test function

常用扩展库

例如：读写excel文件

安装esay_install工具
sudo apt-get install python-setuptools

安装模块
sudo easy_install xlrd
sudo easy_install xlwt

所有内置模块

import sys
sys.modules.keys()

["builtins", "sys", "_frozen_importlib", "_imp", "_warnings", "_thread", "_weakref", "_frozen_importlib_external", "_io", "marshal", "nt", "winreg", "zipimport", "encodings", "codecs", "_codecs", "encodings.aliases", "encodings.utf_8", "_signal", "__main__", "encodings.latin_1", "io", "abc", "_weakrefset", "site", "os", "errno", "stat", "_stat", "ntpath", "genericpath", "os.path", "_collections_abc", "_sitebuiltins", "sysconfig", "idlelib", "idlelib.run", "linecache", "functools", "_functools", "collections", "operator", "_operator", "keyword", "heapq", "_heapq", "itertools", "reprlib", "_collections", "types", "collections.abc", "weakref", "tokenize", "re", "enum", "sre_compile", "_sre", "sre_parse", "sre_constants", "_loc
ale", "copyreg", "token", "queue", "threading", "time", "traceback", "warnings", "tkinter", "_tkinter", "tkinter.constants", "idlelib.autocomplete", "string", "_string", "idlelib.autocomplete_w", "platform", "subprocess", "signal", "msvcrt", "_winapi", "idlelib.multicall", "idlelib.config", "configparser", "_bootlocale", "encodings.gbk", "_codecs_cn", "_multibytecodec", "idlelib.hyperparser", "idlelib.pyparse", "idlelib.calltips", "inspect", "ast", "_ast", "dis", "opcode", "_opcode", "importlib", "importlib._bootstrap", "importlib._bootstrap_external", "importlib.machinery", "textwrap", "idlelib.calltip_w", "idlelib.debugger_r", "idlelib.debugger", "bdb", "fnmatch", "posixpath", "idlelib.macosx", "idlelib.scrolledlist", "idlelib.windows", "idlelib.debugobj_r", "idlelib.rpc", "pickle", "struct", "_struct", "_compat_pickle", "_pickle", "select", "socket", "_socket", "selectors", "math", "socketserver", "idlelib.iomenu", "shlex", "tempfile", "shutil", "zlib", "bz2", "_compression", "_bz2", "lzma", "_lzma", "random", "hashlib", "_hashlib", "_blake2", "_sha3", "bisect", "_bisect", "_random", "locale", "idlelib.stackviewer", "idlelib.debugobj", "idlelib.tree", "idlelib.zoomheight", "pydoc", "importlib.util", "importlib.abc", "contextlib", "pkgutil", "urllib", "urllib.parse"]

内置全局变量：vars()

{"__name__": "__main__", "__doc__": None, "__package__": None, "__loader__": , "__spec__": None, "__annotations__": {}, "__builtins__": }

第三方模块：
anaconda: 数十个常用的第三方模块

内建属性

python类的内建属性和方法

["__class__", "__delattr__", "__dict__", "__doc__", "__format__", "__getattribute__", "__hash__", "__init__", "__module__", "__new__", "__reduce__", "__reduce_ex__", "__repr__", "__setattr__", "__sizeof__", "__str__", "__subclasshook__", "__weakref__"]

__getattribute__例子：

class Person(object):
    def __init__(self, subject1):
        self.subject1 = subject1

    # 属性访问时拦截器，打log
    def __getattribute__(self, obj):
        if obj == "subject1":
            print("log subject1")
        return "redirect python"

    def show(self):
        print("this is Person")

p = Person("python")
print(p.subject1)

内建函数

dir(__builtins__)

["ArithmeticError", "AssertionError", "AttributeError", "BaseException", "BufferError", "BytesWarning", "DeprecationWarning", "EOFError", "Ellipsis", "EnvironmentError", "Exception", "False", "FloatingPointError", "FutureWarning", "GeneratorExit", "IOError", "ImportError", "ImportWarning", "IndentationError", "IndexError", "KeyError", "KeyboardInterrupt", "LookupError", "MemoryError", "NameError", "None", "NotImplemented", "NotImplementedError", "OSError", "OverflowError", "PendingDeprecationWarning", "ReferenceError", "RuntimeError", "RuntimeWarning", "StandardError", "StopIteration", "SyntaxError", "SyntaxWarning", "SystemError", "SystemExit", "TabError", "True", "TypeError", "UnboundLocalError", "UnicodeDecodeError", "UnicodeEncodeError", "UnicodeError", "UnicodeTranslateError", "UnicodeWarning", "UserWarning", "ValueError", "Warning", "ZeroDivisionError", "__debug__", "__doc__", "__import__", "__name__", "__package__", "abs", "all", "any", "apply", "basestring", "bin", "bool", "buffer", "bytearray", "bytes", "callable", "chr", "classmethod", "cmp", "coerce", "compile", "complex", "copyright", "credits", "delattr", "dict", "dir", "divmod", "enumerate", "eval", "execfile", "exit", "file", "filter", "float", "format", "frozenset", "getattr", "globals", "hasattr", "hash", "help", "hex", "id", "input", "int", "intern", "isinstance", "issubclass", "iter", "len", "license", "list", "locals", "long", "map", "max", "memoryview", "min", "next", "object", "oct", "open", "ord", "pow", "print", "property", "quit", "range", "raw_input", "reduce", "reload", "repr", "reversed", "round", "set", "setattr", "slice", "sorted", "staticmethod", "str", "sum", "super", "tuple", "type", "unichr", "unicode", "vars", "xrange", "zip"]

range()

range(stop) # 整数列表
range(start, stop[, step]) # 整数列表

strat: 计数从start开始，默认是从0开始。例如：range(5)等价于range(0, 5)

stop: 到stop结束，但不包括stop。例如：range(0, 5), 返回[0, 1, 2, 3, 4]没有5

step: 每次跳跃的间距，默认为1。例如：range(0, 5)等价于range(0, 5, 1)

map()

map函数会根据提供的函数作为指定序列做映射

map(function, sequence[, sequence, ...]) -> list

function: 一个函数

sequence: 一个或多个序列，取决于function需要几个参数

返回值是一个list

# 函数需要一个参数
map(lambda x: x*x, [1, 2, 3]) # [1, 4, 9]

# 函数需要两个参数
map(lambda x, y: x+y, [1, 2, 3], [4, 5, 6]) # [5, 7, 9]


def f1( x, y ):  
    return (x, y)
l1 = [0, 1, 2, 3, 4, 5, 6]  
l2 = ["Sun", "M", "T", "W", "T", "F", "S"]
l3 = map(f1, l1, l2) 
print(list(l3))
# [(0, "Sun"), (1, "M"), (2, "T"), (3, "W"), (4, "T"), (5, "F"), (6, "S")]

filter()

filter()会对指定序列执行过滤操作

filter(function or None, sequence) -> list, tuple, or string

function: 接受一个参数，返回布尔值True或False

sequence: 序列可以是str,tuple, list

返回值list, tuple, string

filter(lambda x: x%2, [1, 2, 3, 4])
[1, 3]

filter(None, "a")
"a"

reduce()

reduce会对参数序列中对元素进行累积

reduce(function, sequence[, initial]) -> value

function:该函数有两个参数
sequence:序列可以是str，tuple，list
initial:固定初始值

function: 该函数有二个参数

sequence: 序列可以是str, tuple, list

initial: 固定初始值

返回value

reduce(lambda x, y: x+y, [1,2,3,4]) # 10

reduce(lambda x, y: x+y, [1,2,3,4], 5) # 15

reduce(lambda x, y: x+y, ["aa", "bb", "cc"], "dd") # "ddaabbcc"

sorted()

sorted(iterable, cmp=None, key=None, reverse=False) --> new sorted list

iterable: 迭代器

key: 函数

reverse: 正序，倒序

返回一个新的列表

sorted([1, 4, 2, 6, 3, 5]) # [1, 2, 3, 4, 5, 6]

sorted([1, 4, 2, 6, 3, 5], reverse = 1) # 倒序 # [6, 5, 4, 3, 2, 1]

sorted(["dd", "aa", "cc", "bb"]) # ["aa", "bb", "cc", "dd"]

lst = [3, -19, -1, 28, 7, 0, -2, -5, 7, 8, 0 -3, 9, 0, 11]
sorted(lst, key=lambda x: (x >= 0, -x if x >= 0 else x)) # [-19, -5, -3, -2, -1, 28, 11, 9, 8, 7, 7, 3, 0, 0] ​​​​
sorted(lst, key=lambda x: (x >= 0, -abs(x))) # [-19, -5, -3, -2, -1, 28, 11, 9, 8, 7, 7, 3, 0, 0] ​​​​

模块中的__all__的作用

__all__只影响from import *这种导入方式

__all__ = ["test"]

def test():
    print("test")

包、__init__.py的作用

某个文件夹下具有__init.py的，称之为包

__init__.py作用：

package的标识

定义package中的__all__，用来模糊导入

模块的发布和安装

新建一个setup.py写入：

from distutils.core import setup

setup(name="alogy", version="1.0", description="a", author="alogy", py_modules=["suba.aa"]) # suba.aa 包名.模块名

发布：

> python setup.py build

> python setup.py sdist

安装：

> python setup.py install

import搜索路径

import sys
sys.path # sys.path的先后顺序

重新导入模块

模块被导入后，import module不能重新导入模块，需要重新导入

from imp import *
reload("module") # module模块名

pdb是基于命令行的调试工具

运行时启动

python -m pdb xxx.py

l: list 查看运行的代码
n: next 往下行执行
c: continue 继续执行代码直到结束
b 7，b 行数: break 添加断点(通过c执行)
b: 查看所有断点
clear 断点序号: 清除指定断点
s: step 进入当前作用域中
p 变量名: 查看指定变量名的值
a: 查看所有当前作用域的变量名和变量值
q: quit 退出调试
r: return 快速执行到函数最后一行

交互式调试

import pdb
pdb.run("testfun(args)") # 此时会打开pdb调试，注意：先使用s跳转到testfun函数中，然后可以使用

程序里埋点

当程序执行到pbd.set_trace()位置时停下来调试

import pdb

pdb.set_trace()

常用内置模块：
sys: 系统模块, 程序与python解释器的交互, 用于操控python的运行时环境
os: 操作系统模块, 程序与操作系统的交互, 系统操作IO等行为
time，datetime: 时间模块
re: 正则
json: json处理
urllib: 网络处理
random: 随机

不常用内置模块：
itertools: 一些特殊的函数可以操作可迭代对象或者排列组合
copy: 拷贝的函数（赋值一般是传递对象的引用，修改一个对象，会导致其它对象也受到改变）
string: String模块包含大量实用常量和类

Naked

Naked: 一个Python命令行应用程序框架. 可用于执行JS代码

from Naked.toolshed.shell import execute_js, muterun_js
import sys

response = muterun_js("file.js")
if response.exitcode == 0:
  print(response.stdout)
else:
  sys.stderr.write(str(response.stderr))

shutil

用于复制和归档文件和目录树的实用函数。

# 清dist目录
clearDist = (len(sys.argv) == 4 and (sys.argv[3] == "--clear"))
if clearDist:
    shutil.rmtree("./dist/")

subprocess

访问I/O流的子进程

# 编译vue
buildStat = subprocess.call("node build/build.js " + webPath + " " + verPath, shell=True)
if buildStat != 0:
    print("vue 编译错误")
    sys.exit(1)

six

Python 2和3兼容库

import six


def bytes_to_str(s, encoding="utf-8"):
    """Returns a str if a bytes object is given."""
    if six.PY3 and isinstance(s, bytes):
        return s.decode(encoding)
    return s

给程序传递参数

import sys

print(sys.argv) # 接收运行时接受的参数

终止程序运行

import sys
sys.exit(1)