py-snippets.md

Python Snippets

Debug

• debug module imports and show what is importing the current module

  import inspect
  print(inspect.getframeinfo(inspect.getouterframes(inspect.currentframe())[1][0])[0])

• if it says <importlib frozen>, then it means the import came from importlib.reload(..)

Enums

• declare

  from enum import Enum, auto
  class DbgCmdType(Enum):
    Standalone = auto()
    Toggle     = auto()
    IntRange   = auto()
    FloatRange = auto()
    String     = auto()
    ComboBox   = auto()

• iterate over enums

  ((targetTypeEnum.name,targetTypeEnum.value) for targetTypeEnum in UE4TargetType)

Type Checking

• exact: type(py_obj) is list
• inheritance Checking: isinstance(py_obj, SWidget)

Dictionary

• `dict.get(key\[, default\])\: get with optional default fallback
• merge dictionary

  x = dict(a=1, b=2)
  y = dict(b=3, d=4)
  z = {**x, **y}
  # z := {'a': 1, 'b': 3, 'd': 4}, note that value for `b` is taken from the latter dict.

Lists

• unzip or transpose list of tuples

  original = [('a', 1), ('b', 2), ('c', 3), ('d', 4)]
  zip(*original) => (['a', 'b', 'c', 'd'], [1, 2, 3, 4])

• unzip list of Tuples:

  zipper_list = [(1, 'a'), (2, 'b'), (3, 'c')]
  list_a, list_b = zip(*zipper_list)

• flatten list

  a_list = [[1, 2], [3, 4], [5, 6]]
  print(list(itertools.chain.from_iterable(a_list))) # Output: [1, 2, 3, 4, 5, 6]
  print(list(itertools.chain(*a_list))) # Output: [1, 2, 3, 4, 5, 6]
  [*[1,2],*[3]] # Output: [1,2,3]

List Comprehensions

• nested list comprehensions

  # Just think in for-loops syntax. So, If I used for loops for the previous flattening, I’d do something like:
  [y for x in non_flat for y in x]
  # equiv to:
  for x in non_flat:
    for y in x:
      y

Environment

• Registry updating

  from winregistry import WinRegistry
  reg = WinRegistry()
  regPath = r"HKLM\System\CurrentControlSet\Control\Session Manager\Environment"
  return reg.read_value(regPath, envVarName)['data']
  regPath = r"HKCU\Environment"
  reg.write_value(regPath, envVarName, value, valTypeStr)['data']

• get or set environment variables on windows

  klcommon.getSysEnvVar(envVarName)
  klcommon.setSysEnvVar(envVarName, value, valTypeStr='REG_EXPAND_SZ')
  klcommon.getUserEnvVar(envVarName)
  klcommon.setUserEnvVar(envVarName, value, valTypeStr='REG_EXPAND_SZ')

• Python interpreter version number

  import sys
  sys.version_info
  print(sys.version)
  print(sys.executable)
  import os
  print(os.__file__)

Path Manipulations

• convert to relative

  ue4_asset_dir = '/Game/' + Path(os.path.relpath(capself.animAssetDirPicker.get_directory(), ue.get_content_dir()))

• normalize path

  Path('../mydir').absolute()

• convert to forward slashes only

  Path(...).as_posix()

• join paths together

  Path('/engine')  / Path('/content')

Directory

• list directory contents

  import os
  for file in os.listdir("/mydir"):
    if file.endswith(".txt"):
      print(file)

• list directory contents with filter

  import os
  import glob
  os.chdir("/mydir")
  for file in glob.glob("*.txt"):
    print(file)

• iterate directory hierarchy

  import os
  for root, dirs, files in os.walk("/mydir"):
    for file in files:
      if file.endswith(".txt"):
        print os.path.join(root, file)

• list immediate child subdirectories

  next(os.walk('.'))[1]

• References

  • http://www.diveintopython.net/file_handling/os_module.html
  • https://docs.python.org/2/library/filesys.html
  • https://stackoverflow.com/questions/973473/getting-a-list-of-all-subdirectories-in-the-current-directory