ShuJuQiu: PythonNotes

dreamable/PythonNotes
ID	标题	笔记	Tag
3	目录名改变后venv必须重新初始化	我将engine_py3重新命名为engine后，不工作了！python转为了系统的py2。必须重新初始化venv环境。例如 `python3.8 -m venv env` 这是因为，路径被写进去了。 ./pyftmerge:#!/home/netro/codes/chao_dev/engine_py3/env/bin/python3.8 ./f2py3:#!/home/netro/codes/chao_dev/engine_py3/env/bin/python3.8 ./activate.fish:set -gx VIRTUAL_ENV "/home/netro/codes/chao_dev/engine_py3/env" ./activate:VIRTUAL_ENV="/home/netro/codes/chao_dev/engine_py3/env" ./hyper:#!/home/netro/codes/chao_dev/engine_py3/env/bin/python3.8 ./ttx:#!/home/netro/codes/chao_dev/engine_py3/env/bin/python3.8 ./pyrsa-verify:#!/home/netro/codes/chao_dev/engine_py3/env/bin/python3.8 ./futurize:#!/home/netro/codes/chao_dev/engine_py3/env/bin/python3.8 ./activate.csh:setenv VIRTUAL_ENV "/home/netro/codes/chao_dev/engine_py3/env" ./pyrsa-sign:#!/home/netro/codes/chao_dev/engine_py3/env/bin/python3.8 ./fixup_translate_v3beta1_keywords.py:#!/home/netro/codes/chao_dev/engine_py3/env/bin/python3.8 可见activate中写死了路径。改变后，找不到了。有些stupid。可以用链接，例如 `ln -s engine_py3 engine`。可以work
2	Python3 + MongoDB bug	遇到一个奇怪的问题，在Python3中，调用MongoDB。Sorting会影响结果。基本代码 `order = pymongo.DESCENDING if self.descending else pymongo.ASCENDING items = self.tb.find(cond).sort(self.uid,order).limit(self.limit) logging.info(f"There are {items.count()} items") for idx,t in enumerate(items): logging.info(f"Working on {idx}-th item: {t[self.uid]}")` 问题：当order为descending，limit> # of records, hang after 100 records 当order为ascending的时候，问题不存在当limit <= # of records时候，问题不存在只对一个collection有此问题，其它类似collection没有此问题存在{uid: -1}的index，添加{uid:1}的index无帮助找不到原因，可能是某个地方的bug。采用ascending order绕开了这个问题。	Python MongoDB
1	cython	python vs cpython vs cython python: 语言 cpython: Python的解释器，用C实现的，也有用Java实现的Jython cython：优化器，将python编译为C语言，提高运行速度 superset language python + C extension install (version 0.29.21) `sudo pip install cython` setup.py `from setuptools import setup from Cython.Build import cythonize setup( name='Hello world app', ext_modules=cythonize(["hello.py","utils.py","config.py"],annotate=True), zip_safe=False, )` `python setup.py build_ext --inplace` build error in `~/engine`: ERROR: error: [Errno 2] No such file or directory: 'engine/hello.so' in `~/engine/tmp`: OK in `~/engine2': OK remove `__init__.py` solves the problem.