Vim's Omnicompletion with Python just doesn't work

Question

I\'ve searched around for an hour, both on Stack Overflow and elsewhere. Alas! Please help. Vim\'s omnicompletion just doesn\'t work.

1. I have Vim 7.

Answer 1

Sounds like the questioner has long since gone to the dark side*, but for what it's worth I've just had this symptom, and in my case the cause was that a module I was using relied on Python 2.7 but my version of Vim was compiled with Python 2.5.

To diagnose I tried :python import mymodule, which failed with an error about importing a dependent module. Then :python import dependentmodule which failed with the next step in the chain. And so on & so on, until it failed trying to import a system module that was new since Python 2.7. Problem found.

To solve, I just did sudo port install vim +python27. But that's for OSX. YMMV.

(* I'm kidding. Emacs users are our friends. It's the people programming in Notepad we all have to save...)

Answer 2

You are not doing anything wrong. Python omni completion does not use a tags file. This is on purpose. You do not need to make a tags file for omni completion. You can still make a tags file for the usual tag-stack jumping, but it is ignored by omni completion.

It took me a long time to figure this out because C omni completion does use a tags file. Python omni completion works differently.

You can quickly observe this behavior by attempting omni completion in a Python file with python filetype and then with c filetype.

First :set filetype=python (this is the default), then :echo &omnifunc. Omni complete ignores the tags file because &omnifunc is python3complete#Complete, which does not use the tags file.

Now :set filetype=c and :echo &omnifunc. Vim treats the Python script as a C file, so &omnifunc is ccomplete#Complete, which uses the tags file. Of course treating Python files like C files is not the solution!

Below are:

• two examples of how to do Python omni completion
• where the &omnifunc (syntaxcomplete#Complete) Vimscripts are implemented
• how preview window behavior differs between a tags file preview (:pta) and the omni complete preview.

There is also tag completion: <C-x><C-]>. If you already use a tags file and want Vim to complete using those tags, <C-x><C-]> is the completion you are looking for, not <C-x><C-o>.

But I encourage you to read on. Omni completion does more than tag completion:

1. Omni completion recognizes module names and auto completes using the correct Python syntax. For example, if you import numpy as np, then np.a<C-x><C-o> presents a menu of numpy functions starting with letter 'a'. Tag completion only auto-completes a match in the tags file.
2. Omni completion populates the preview window with documentation. Tag completion does not open a preview window.
3. And, for Python, omni completion does not require updating a tags file!

Example 1: omni complete to match a pattern in this file

Python omni completion requires that the Python script you are editing is working Python code. Here is a simple example with a local variable:

foo_name_I_expect_omni_completion

This one-line script does not run (my variable name is not defined), so if I edit this script and attempt to omni complete:

foo_name_I_expect_omni_completion
foo_name_<C-x><C-o>

I get the "Pattern not found" message.

This is infuriating because the pattern it should match is literally on the line above!

But all we need to make omni completion work is change this to valid Python code:

foo_name_I_expect_omni_completion = 2
foo_name_<C-x><C-o>

Now omni completion works!

Example 2: omni complete to match a pattern in an imported module

As a second example, omni completion also works if the pattern to match is in another file, as long as that file is visible (with an import statement) to the script being edited.

Again, I'll use foo_name_I_expect_omni_completion=2. I save the file with this one-liner as mymodule.py. Now in a new file, example.py, I import mymodule:

import mymodule

Once I've typed import mymodule, i_<C-x><C-o> works on the module name:

import mymodule
mym<C-x><C-o>

Omni complete turns this into:

import mymodule
mymodule.

and a menu of patterns pops up (see :h completeopt for configuring the menu behavior), at which point I can do the usual <C-n><C-y> to select the first item on the list and exit omni complete back to insert mode.

import mymodule
mymodule.foo_name_I_expect_omni_completion

If omni complete seems broken, check that the imported module is executable

If omni completion seems unable to see an imported module, it is because the module you are importing is not executable.

Unlike the toy example above, this is hard to track down if the imported module also imports packages and you have multiple versions of Python with different packages installed in each version.

For example, I have 3.6 and 3.7 installed, but I'd only installed a certain package on 3.6. And that same package was imported by the module I was importing in the script I was trying to edit with omni complete.

Somehow, python3.6 was my default python3 from bash, but python3.7 was my default from Vim. So the module seemed valid when I ran it from bash, because my python3.6 installation had the necessary package.

Check which version of Python Vim is using:

:py3 print(sys.version)

Also check sys.path, as explained in the answer by codeape:

:py3 print(sys.path)

I have many installations of Python, and every Python installation has its own USER_SITE path.

:py3 import site; print(site.USER_SITE)

I use one USER_SITE folder and find a way to point each Python installation at it. For the Python installation Vim omni-complete uses, I do this by editing the PYTHONPATH environment variable.

In my case, my one active USER_SITE is for Python 3.7, and Vim is using Python 3.6, so I put this in my .bashrc:

# Python USERSITE folder
pkg=$HOME/.local/lib/python3.7/site-packages/

# Add to PYTHONPATH for Vim omni-complete to see packages I wrote
PYTHONPATH=$PYTHONPATH:$pkg

Documentation

I figured this out by tracking down the Vim scripts that do the completion.

From Vim help:

:h compl-omni-filetypes

The file used for {filetype} should be autoload/{filetype}complete.vim in 'runtimepath'. Thus for "java" it is autoload/javacomplete.vim.

These autoload/{filetype}complete.vim files are in your Vim installation. For example, here are my C and Python files:

/usr/share/vim/vim81/autoload/ccomplete.vim
/usr/share/vim/vim81/autoload/python3complete.vim

Alternatively, call :echo &omnifunc and find the Vimscript on GitHub: https://github.com/vim/vim/blob/master/runtime/autoload/

I started to suspect my fundamental misunderstanding of the problem when I found the word tag does not appear in the python3complete.vim file :)

Omni complete has a special preview behavior

I've always been confused by the behavior of the preview window. Omni complete has a different preview behavior from tags.

First, to get a preview window with omni complete, Vim completeopt option must contain preview and either menu or menuone.

completeopt defaults to menu,preview. To set options explicitly, e.g., to use menuone instead on menu:

set completeopt=menuone,preview

menuone makes a menu always appear, even if there is only one pattern that matches. With menu, the menu does not appear for a single match, so neither does the preview window. Using menuone guarantees the preview window pops up.

Turn off preview to prevent the window split during omni complete:

set completeopt-=preview

Notice that the preview behavior for omni complete (which opens when you highlight a menu item) is different from the preview behavior for tags (which you open with <C-w>} or :pta)

• tag-preview opens the code in the preview window
• omni-complete-preview opens documentation

Omni complete's preview shows different things depending on the item highlighted in the completion menu. If it is a variable, the pydoc for its datatype is shown; if it is a function, its docstring is shown.

Answer 3

Having updated to Fedora 16 (but still compiling vim from source), omni completion stopped working with the same message as above. I "fixed" it by re-maping the keys.

inoremap <C-space> <C-x><C-o>

in ~/.vimrc and now it works again.

Answer 4

Have you tried using <C_x><C-]> ?

Answer 5

I used supertab (http://www.vim.org/scripts/script.php?script_id=1643)

Since C-x C-o is a bit frustrating to use

in .vimrc:

let g:SuperTabDefaultCompletionType = "<c-x><c-o>"

then just use Tabb for omnicompletion

Answer 6

What module contains the symbol you are trying to complete? Is it in the python stdlib? Or is it a third-party module?

Make sure that the module/package is in the PYTHONPATH.

In Vim, do:

:python import sys
:python print sys.path

To add the module's directory:

:python sys.path.append("/path/to/directory/")