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python

升级PIP

python -m pip install --upgrade pip

代理

easy_install -i https://pypi.douban.com/simple/ requests
pip install -i https://pypi.douban.com/simple/ requests

文件头

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

# or

#! /usr/bin/env python
# coding=utf-8

遍历文件夹

import os
for root, dirs, files in os.walk(top, topdown=False):
    for name in files:
        os.remove(os.path.join(root, name))
    for name in dirs:
        os.rmdir(os.path.join(root, name))

运行时相关

# 当前文件夹
os.getcwd()
# 当前脚本路径
file_path  = os.path.realpath(__file__)
# 当前脚本文件夹
os.path.dirname(file_path)

生成pyc文件

用py_compile模块

import py_compile
py_compile.compile(file_path)

也可以直接执行命令转换当前所有py文件,使用到compileall模块

python -m compileall xxx.py
python -m compileall .

生成的pyc可以跨平台使用,但是只能这样用python xxx.pyc,而不能使用./xxx.pyc执行,因为缺少了shebang的支持,不过貌似Binfmt_misc可以解决这个问题,ubuntu下apt-get install binfmt-support可以直接安装。

文件操作高级封装

10.10. shutil — High-level file operations

环境变量

15.1.1. Process Parameters¶

import os

for k, v in os.environ.items():
    print "%s => %s" % (k, v)

# Note Calling putenv() directly does not change os.environ, so it’s better to modify os.environ.
os.getenv('PATH')
os.putenv('GO15VENDOREXPERIMENT', '0')

main的写法

if __name__ == "__main__":

子进程

Python 产生子进程的方法有:

  1. os.popen
  2. subprocess.popen
  3. os.system
  4. os.fork
  5. os.spawnv
  6. os.fork

sys

import sys

# 获取参数
print sys.argv

# 获取 path
print sys.path

# 获取已载入模块
print sys.modules

# 执行信息,发生异常时可以获取到
print sys.exec_info()

标准流

  1. sys.stdin
  2. sys.stdout
  3. sys.stderr

提供文件方法的对象都可以作为标准流:

带 read() 方法的对象可以赋值给 sys.stdin; read() 为输入流提供数据 带 write() 方法的对象可以赋值给 sys.stdout; 所有标准输出都发给 write() 方法。

class Input(object):
    def read(self):
        return 'hello, world\n'
class Output(object):
    def write(self, s):
        f = open('1.txt', 'w')
        f.write(s)
        f.close()

sys.stdin = Input()
sys.stdin.read() # 'hello, world'
sys.stderr = Input()
sys.stderr.read() # 'hello, world'
sys.stdout = Output()
sys.stdout.write('hello, world\n') #生成文件 1.txt,输入文本 'hello, world\n'

版本比较

Python的版本比较有很多种方法,StrictVersion、LooseVersion还有NormalizedVersion。不过在 PEP 386已经不推荐使用StrictVersion和LooseVersion了。

Note that LooseVersion and StrictVersion have been deprecated under PEP 386 and will at some point be replaced by NormalizedVersion.

安装verlib

pip install -i https://pypi.douban.com/simple/ verlib

使用版本比较的功能。

from verlib import NormalizedVersion
NormalizedVersion("1.2b1") < NormalizedVersion("1.2") #True

检查pid是否在运行

How to check if there exists a process with a given pid?

import errno
import os
import sys

def pid_exists(pid):
    """Check whether pid exists in the current process table.
    UNIX only.
    """
    if pid < 0:
        return False
    if pid == 0:
        # According to "man 2 kill" PID 0 refers to every process
        # in the process group of the calling process.
        # On certain systems 0 is a valid PID but we have no way
        # to know that in a portable fashion.
        raise ValueError('invalid PID 0')
    try:
        os.kill(pid, 0)
    except OSError as err:
        if err.errno == errno.ESRCH:
            # ESRCH == No such process
            return False
        elif err.errno == errno.EPERM:
            # EPERM clearly means there's a process to deny access to
            return True
        else:
            # According to "man 2 kill" possible error values are
            # (EINVAL, EPERM, ESRCH)
            raise
    else:
        return True

Renference:

学习Python Compare version strings Working with versions PEP 386 -- Changing the version comparison module in Distutils

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