Auto completion popup opens with zero character match in Inferior Python mode (comint repl)

Question

When I enter an IPython repl via python-start-or-switch-repl, I get annoying auto completion behavior where the completions popup opens with zero characters entered. If I type one character and erase it the popup opens and stays open starting with '%%!', '%%HTML', etc. If I type a function call like print('hello') and hit enter, Autocompletion inserts '%%!' at the end of my input and I end up entering print('hello')%%!. Auto completion works fine in all other buffers.

Here are the results from M-x describe-mode:

Minor modes enabled in this buffer: Anzu Company Compilation-Shell Evil-Local
Evil-Surround Font-Lock Show-Smartparens Smartparens Spacemacs-Leader-Override
Term-Cursor Undo-Tree Yas

The major mode is Inferior Python mode defined in python.el:

Major mode for Python inferior process.
Runs a Python interpreter as a subprocess of Emacs, with Python
I/O through an Emacs buffer.  Variables ‘python-shell-interpreter’
and ‘python-shell-interpreter-args’ control which Python
interpreter is run.  Variables
‘python-shell-prompt-regexp’,
‘python-shell-prompt-output-regexp’,
‘python-shell-prompt-block-regexp’,
‘python-shell-font-lock-enable’,
‘python-shell-completion-setup-code’,
‘python-shell-completion-string-code’,
‘python-eldoc-setup-code’,
‘python-ffap-setup-code’ can
customize this mode for different Python interpreters.

This mode resets ‘comint-output-filter-functions’ locally, so you
may want to re-add custom functions to it using the
‘inferior-python-mode-hook’.

EDIT: Here are some company-mode details:

Company 0.9.13

company-backends: (php-extras-company company-bbdb company-semantic company-cmake company-capf company-clang company-files
                    (company-dabbrev-code company-gtags company-etags company-keywords)
                    company-oddmuse company-dabbrev)

Used backend: company-capf
Value of c-a-p-f: (lsp-completion-at-point python-completion-at-point t)
Major mode: python-mode
Prefix: ""

EDIT: @dalanicolai requested this info:

python-shell-interpreter-args is a variable defined in ‘python.el’.

Its value is "-i --simple-prompt"
Original value was "-i"
Local in buffer *Python*; global value is "-i"

Answer 1

You’re using company-mode for completion, so you should consult the company-mode documentation (this manual is also available inside the Emacs Info viewer, type C-h i to start it).

In particular, language–specific suggestions come from a language–specific backend. You can check which backends are in use by checking the value of the company-backends variable, as well as the `completion-at-point-functions variable (both of which you should include in your question).

Once you figure out where Company is getting the suggestions, you will have figured out how to configure it properly.

Answer 2

The spacemacs python layer is setting company-minimum-prefix-length to 0:

spacemacs python layer:

(defun python/post-init-company ()
  ;; backend specific
  (add-hook 'python-mode-local-vars-hook #'spacemacs//python-setup-company)
  (spacemacs|add-company-backends
    :backends (company-files company-capf)
    :modes inferior-python-mode
    :variables
    company-minimum-prefix-length 0
    company-idle-delay 0.5)
  (when (configuration-layer/package-used-p 'pip-requirements)
    (spacemacs|add-company-backends
      :backends company-capf
      :modes pip-requirements-mode)))

This layer overrides my use of setq-local in a python-inferior-mode-hook in my init file as well as anything done with M-x customize-variable. The only fix as of now is using M-x set-variable every time I open a python-inferior-mode buffer. Using M-x python-shell-restart resets the variable to 0 and I have to set it again.