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    What does this mean: "this is done to prevent directories with a common name, such as string, from unintentionally hiding valid modules that occur later on the module search path"?
    – Carl G
    Commented Jan 25, 2014 at 4:43
  • 129
    @CarlG Python searches a list of directories to resolve names in, e.g., import statements. Because these can be any directory, and arbitrary ones can be added by the end user, the developers have to worry about directories that happen to share a name with a valid Python module, such as 'string' in the docs example. To alleviate this, it ignores directories which do not contain a file named _ _ init _ _.py (no spaces), even if it is blank.
    – Two-Bit Alchemist
    Commented Mar 7, 2014 at 20:56
  • 257
    @CarlG Try this. Make a directory called 'datetime' and in it make two blank files, the init.py file (with underscores) and datetime.py. Now open an interpreter, import sys, and issue sys.path.insert(0, '/path/to/datetime'), replacing that path with the path to whatever directory you just made. Now try something like from datetime import datetime;datetime.now(). You should get an AttributeError (because it is importing your blank file now). If you were to repeat these steps without creating the blank init file, this would not happen. That's what it's intended to prevent.
    – Two-Bit Alchemist
    Commented Mar 7, 2014 at 21:03
  • 1
    All I get is ImportError: attempted relative import with no known parent package. My structure: /PyToHtml init.py pytohtml.py test.py where test.py has: from .pytohtml import HTML
    – João Vitor Barbosa
    Commented May 11, 2022 at 13:20