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Python Learning Notes

Always check your code thoroughly before asking for help. Ref: request Cross Site error caused by []

system

  1. use pyenv to get around root privileges
  2. use Anaconda to get around compiling restriction
  3. Anaconda missing packages:
  • plotly

Crontab

Allow relative Path in crontab:

  1. crontab can use cd to change working directory

  2. #! can be changed to pyenv .shim

  3. .py file need to be excutable chmod +x

  4. Sample crontab command

     . ~/.bashrc
 cd /home/liuyidh/laviex/pyreport/
 ./ALL_report.py`

Python:

  1. use map() to simplify things

  2. use list comprehension to flatten a nested list/dict

     [b for dic in [dict1, dict2, dict3] for (a,b) in dic.items()]

  3. use dict / list comprehension for powerful process:

     info = {k: [x.strip() for x in v] for (k, v) in info.iteritems()}
 
 

 Use a dictionary when you have a set of unique keys that map to values.
 Use a list if you have an ordered collection of items.
 Use a set to store an unordered set of items.

  4. filter empty string:

     str_list = filter(None, str_list)

  5. use functools.partial to freeze/set certain arguments

  6. remember to close file to finish writing.

  7. syntax brackets error due to sublime autocompletion

  8. memory release

    • del + gc.collect()
    • multiprocessing
    • divide into smaller chunks then use shell script to run one by one

  9. class Object does not update automatically if you revise the class after the object is created.

  10. Fucntions: reuse, readability, avoid redundancy

    • KimPeek 2 years ago
    • Functions should be small, sharp tools that do one thing well. This is a guideline, not a hard rule, but you should generally make a new function for each code block. Every loop, try/except block, whenever you indent more than 3 times, and anytime you are doing more than one thing.

Pandas:

  1. use astype(float) to change stype
  2. pandas-datareader 0.5.0 not available from conda, use pip instead, no need to downgrade

lxml:

  1. be careful with JS re-written attributes and capitalization.
  2. be careful with text with /t/n spaces
  3. be careful wih variable explorer

Web2py:

  1. how to uWSGI
  2. how to multiple domains
  3. use nohup xxxx & to run background or use screen to run ssh tunneled python admin
  4. use crontab @reboot to start web2py.py -K app
  5. define table
  6. use request.args to dynamicly define variables (mailer headers etc.)
  7. request.requires_https() includes redirect and session.secure() link