'import x' vs “ 'from x import y' and 'import x.y' ”

Question

I tried

from urllib import request 
mine = request.Request()

and

import urllib.request
mine = urllib.request.Request()

They both work fine. But

import urllib
mine = urllib.request.Request()

gives me

AttributeError: 'module' object has no attribute 'request' 

Shouldn't it work too considering request is an attribute of urllib? If it isn't, why do the previous statements work? I'm using python 3.4.3.

Answer 1

Python, when importing a package, doesn't import all of the contents of that package - it imports the contents of the package's __init__.py file. (Or, at least, it seems to.)

I just did some tests with this, and I found the following:

>>> import urllib
>>> dir(urllib)
['__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__path__', '__spec__']

As you can see, request , error , parse , response , and robotparser are not there. It only imported the __init__.py file.

So, to further test, I took a look at tkinter .

Here is tkinter's folder:

And so, to test the theory that only __init__.py is initially accessible, here are some commands with relation to tkinter:

>>> import tkinter
>>> tkinter.font
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'tkinter' has no attribute 'font'
>>> tkinter.test
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'tkinter' has no attribute 'test'
>>> tkinter.test.support
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'tkinter' has no attribute 'test'
>>> dir(tkinter)
['ACTIVE', 'ALL', 'ANCHOR', 'ARC', 'BASELINE', 'BEVEL', 'BOTH', 'BOTTOM', 'BROWSE', 'BUTT', 'BaseWidget', 'BitmapImage', 'BooleanVar', 'Button', 'CASCADE', 'CENTER', 'CHAR', 'CHECKBUTTON', 'CHORD', 'COMMAND', 'CURRENT', 'CallWrapper', 'Canvas', 'Checkbutton', 'DISABLED', 'DOTBOX', 'DoubleVar', 'E', 'END', 'EW', 'EXCEPTION', 'EXTENDED', 'Entry', 'Event', 'FALSE', 'FIRST', 'FLAT', 'Frame', 'GROOVE', 'Grid', 'HIDDEN', 'HORIZONTAL', 'INSERT', 'INSIDE', 'Image', 'IntVar', 'LAST', 'LEFT', 'Label', 'LabelFrame', 'Listbox', 'MITER', 'MOVETO', 'MULTIPLE', 'Menu', 'Menubutton', 'Message', 'Misc', 'N', 'NE', 'NO', 'NONE', 'NORMAL', 'NS', 'NSEW', 'NUMERIC', 'NW', 'NoDefaultRoot', 'OFF', 'ON', 'OUTSIDE', 'OptionMenu', 'PAGES', 'PIESLICE', 'PROJECTING', 'Pack', 'PanedWindow', 'PhotoImage', 'Place', 'RADIOBUTTON', 'RAISED', 'READABLE', 'RIDGE', 'RIGHT', 'ROUND', 'Radiobutton', 'S', 'SCROLL', 'SE', 'SEL', 'SEL_FIRST', 'SEL_LAST', 'SEPARATOR', 'SINGLE', 'SOLID', 'SUNKEN', 'SW', 'Scale', 'Scrollbar', 'Spinbox', 'StringVar', 'TOP', 'TRUE', 'Tcl', 'TclError', 'TclVersion', 'Text', 'Tk', 'TkVersion', 'Toplevel', 'UNDERLINE', 'UNITS', 'VERTICAL', 'Variable', 'W', 'WORD', 'WRITABLE', 'Widget', 'Wm', 'X', 'XView', 'Y', 'YES', 'YView', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__path__', '__spec__', '_cnfmerge', '_default_root', '_exit', '_flatten', '_join', '_magic_re', '_setit', '_space_re', '_splitdict', '_stringify', '_support_default_root', '_test', '_tkerror', '_tkinter', '_varnum', 'constants', 'getboolean', 'getdouble', 'getint', 'image_names', 'image_types', 'mainloop', 're', 'sys', 'wantobjects']

Noticing mainloop in the dir response, I checked __init__.py - sure enough, mainloop() is defined there.

So, in answer to your question, Python only loads urllib 's __init__.py file when you do import urllib - not request.py .

edit: As another point, in dir(tkinter) , there were some variables defined in tkinter.constants , and not __init__.py . That's because in tkinter 's __init__.py , it imports tkinter.constants with from tkinter.constants import * .