variable with underscore

• Python Docs - Private Variables and Class-local References
• The meaning of a single- and a double-underscore before an object name in Python
• Underscore vs Double underscore with variables and methods
• Private, protected and public in Python

@nmichaels's answer:

- _single_leading_underscore: weak "internal use" indicator.  E.g. "from M
  import *" does not import objects whose name starts with an underscore.

- single_trailing_underscore_: used by convention to avoid conflicts with
  Python keyword, e.g.

  Tkinter.Toplevel(master, class_='ClassName')

- __double_leading_underscore: when naming a class attribute, invokes name
  mangling (inside class FooBar, __boo becomes _FooBar__boo; see below).

- __double_leading_and_trailing_underscore__: "magic" objects or
  attributes that live in user-controlled namespaces.  E.g. __init__,
  __import__ or __file__.  Never invent such names; only use them
  as documented.

property method

• Python Docs - property
• Python @property versus getters and setters
• Python进阶之“属性（property）”详解
• Properties vs. Getters and Setters

计算目录的md5

也就是遍历目录, 计算所有文件内容合并后的md5值。

注意: 保证遍历目录的路径是一致的, 否则跨平台遍历方式不一致导致md5不同。

见Simiki中的实现: Add directory md5 hash function, 另外, 这个可能还需要考虑内存溢出的情况? TODO

另外可参考:

• How do I get the MD5 sum of a directory's contents as one sum?
• Getting the SHA-1 (or MD5) hash of a directory (Python recipe)

pip install from git repo

$ pip install -e git+https://github.com/username/projname.git#egg=projname

参考:

• pip install from github repo branch
• pip doc - VCS Support

virtualenv对系统级包的策略

最近发现使用virtualenv进入一个隔离环境时, 每次cd切换目录都会报错, 原因是autojump(py写的)模块找不到。

排查后发现是系统级的python包目录不在sys.path中。

看了virtualenv的changelog发现这个是在1.7版本做的变更:

• virtualenv-1.7 之前, 默认策略是把把系统包路径也加入 sys.path. 有 --no-site-packages 在创建虚拟环境时, 可以不加入系统包路径.
• virtualenv-1.7和之后, 默认策略是上面的 --no-site-packages. 并且增加了新选项 --system-site-packages, 即上面情况的默认策略.

具体可以看看virtualenv 的 changelog

我之前应该很长一阵子都处于1.7之前的版本, 最近才作了下升级.

list和dict释放空间

list:

• how to release used memory immediately in python list?
• python memory del list[:] vs list = []

• a = [] 新赋值, 其它引用不变
• del a 删除a, 其它引用不变
• del a[:] 清空a的元素, 所有引用和a保持一样变化, 也为空

dict:

• Difference between dict.clear() and assigning {} in Python
• Does dictionary's clear() method delete all the item related objects from memory?

• d = {} 新赋值，其它引用不变
• del d 删除d, 其它引用不变
• d.clear() 清空d的元素, 所有引用和d保持一样变化, 也为空