Why does this Python3 module appear to perform a relative import of itself?

Question

If I create a module named 'json.py' with the following contents:

#! python
import json as _json
JSONDecoder = _json.JSONDecoder

..shouldn't the 'import json as _json' statement perform an absolute import, and therefore provide the python standard-lib JSON module?

..instead, if I execute or import this module, I get:

$ python --version
Python 3.4.0
$ python relative_import/json.py 
Traceback (most recent call last):
  File "relative_import/json.py", line 3, in 
    import json as _json
  File "/home/silver/Projects/relative_import/json.py", line 6, in 
    JSONDecoder = _json.JSONDecoder
AttributeError: 'module' object has no attribute 'JSONDecoder'
$

..which shows that 'json' is importing itself (a relative import). ..I imagine I'm missing something -- python's import system has always made natural and intuitive sense to me, but in this case I'm lost.

Edit: I'm using python 3.4

Edit: For anyone interested, this is what occurred: I have a package which includes a module called 'json', which replaces the system 'json'. This is fine (IMO), however, I also started a script that was in the same package folder (temporarily) but not meant to ultimately be a part of the same module. Thus, the following occurred:

I run my script, packagename/foo.py
python adds packagename folder to sys.path
foo.py imports packagename.json
packagename.json imports json (which would normally be the system json)
first entry on sys.path is the packagename folder, and 'json' is imported from there
my json.py continues loading after the import, and runs into errors (because it's dealing with itself, not the system json module)

Solution: Move the script to my package's 'bin' folder, or, if I want it to be a part of the package proper, use python -m packagename.foo

Thank you, @Martijn Pieters.

Martijn Pieters Martijn Pieters · Accepted Answer · 2014-10-01T13:51:01

It is doing an absolute import.

The directory the main script lives in is added to sys.path, and as a result the first json found is your script. You are running python relative_import/json.py and Python thus adds relative_import/ to sys.path.

Note that the main script is named __main__, so import json does import the script file as a separate, new module object. Your code is in effect loaded twice.

See the Interface options documentation:

If the script name refers directly to a Python file, the directory containing that file is added to the start of sys.path, and the file is executed as the __main__ module.

Why does this Python3 module appear to perform a relative import of itself?

1 Answers