IDE Features

Projects

Elpy supports the notion of projects, a related collection of files under a common directory. This common directory is called the project root. A number of Elpy’s commands work on all files inside the project root.

C-c C-f (elpy-find-file)

Find a file in the current project. This uses a search-as-you-type interface for all files under the project root.

A prefix argument enables “do what I mean” mode. On an import statement, it will try to open the module imported. Elsewhere in a file, it will look for an associated test or implementation file, and if found, open that. If this fails, either way, it will fall back to the normal find file in project behavior.

If the current file is called foo.py, then this will search for a test_foo.py in the same directory, or in a test or tests subdirectory. If the current file is already called test_foo.py, it will try and find a foo.py nearby.

This command uses projectile or find-file-in-project under the hood, so you need one of them to be installed.

C-c C-s (elpy-rgrep-symbol)

Search the files in the current project for a string. By default, this uses the symbol at point. With a prefix argument, it will prompt for a regular expression to search.

This is basically a grep -r through the project.

In addition to these two commands, elpy-check also supports optionally checking all files in the current project.

Elpy’s idea of the project root and which files belong to a project and which don’t can be influenced as well.

M-x elpy-set-project-root

Set the current project root directory. This directory should contain all files related to the current project.

elpy-project-ignored-directories (Customize Option)

When Elpy searches for files in the current project, it will ignore files in directories listed here.

elpy-project-root-finder-functions (Customize Option)

To find the project root, Elpy can utilize a number of heuristics. With this option, you can configure which are used.

To configure Elpy specifically for a single project, you can use Emacs’ Directory Variables. Elpy provides a simple interface to this.

M-x elpy-set-project-variable

Set or change the value of a project-wide variable. With a prefix argument, the value for the variable is removed.

This only takes effect in new buffers.

Completion

When you type Python code, Elpy will try and figure out possible completions and provide them in a suggestion window. If Elpy doesn’t do so automatically, you can force it to complete right where you are.

M-TAB (elpy-company-backend)

Provide completion suggestions for a completion at point.

You can use cursor keys or M-n and M-p to scroll through the options, RET to use the selected completion, or TAB to complete the common part.

On any completion option, C-d or <f1> will display a temporary window with documentation. C-w will display a temporary window showing the source code of the completion to get some context.

Elpy uses Company Mode for the completion interface, so its documentation is a good place for further information.

elpy-get-info-from-shell (Customize Option)

If t, use the shell to gather docstrings and completions. Normally elpy provides completion and documentation using static code analysis (from jedi). With this option, elpy will add the completion candidates and the docstrings from the associated python shell; This activates fallback completion candidates for cases when the static code analysis fails.

Interactive Python

Emacs can run a Python interpreter in a special buffer, making it much easier to send code snippets over. Elpy provides additional functionality to seamlessly work with interactive Python in a style similar to ESS.

Interpreter Setup

Elpy uses the Python interpreter setup from the Emacs python package. This section briefly summarizes some common setups; add the one you need to your .emacs file. Note that the code below (and Elpy in general) require at least Emacs 24.4.

Use the Python standard interpreter (default):

(setq python-shell-interpreter "python"
      python-shell-interpreter-args "-i")

Use Jupyter console (recommended for interactive Python):

(setq python-shell-interpreter "jupyter"
      python-shell-interpreter-args "console --simple-prompt"
      python-shell-prompt-detect-failure-warning nil)
(add-to-list 'python-shell-completion-native-disabled-interpreters
             "jupyter")

Use IPython:

(setq python-shell-interpreter "ipython"
      python-shell-interpreter-args "-i --simple-prompt")

Note that various issues with plotting have been reported when running IPython 5 in Emacs under Windows. We recommend using Jupyter console instead.

If you have an older version of IPython and the above code does not work for you, you may also try:

(setenv "IPY_TEST_SIMPLE_PROMPT" "1")
(setq python-shell-interpreter "ipython"
      python-shell-interpreter-args "-i")

As an IPython_ user, you might be interested in the `Emacs IPython
Notebook`_ or an `Elpy layer`_ for Spacemacs_, too.

Note for MacOS users: In some configurations, display artifacts (lines of ^G s) can appear in the shell. This can be fixed by prepending -c exec('__import__(\\'readline\\')') to python-shell-interpeter-args (e.g. (setq python-shell-interpreter-args "-c exec('__import__(\\'readline\\')') -i") for python)

The Shell Buffer

C-c C-z (elpy-shell-switch-to-shell)

Switch to buffer with a Python interpreter running, starting one if necessary.

By default, Elpy tries to find the root directory of the current project (git, svn or hg repository, python package or projectile project) and starts the python interpreter here. This behaviour can be suppressed with the option elpy-shell-starting-directory.

elpy-shell-starting-directory (Customize Option)

Govern the directory in which Python shells will be started. Can be 'project-root (default) to use the current project root, 'current-directory to use the buffer current directory, or a string indicating a specific path.

M-x elpy-shell-toggle-dedicated-shell

By default, python buffers are all attached to a same python shell (that lies in the *Python* buffer), meaning that all buffers and code fragments will be send to this shell. elpy-shell-toggle-dedicated-shell attaches a dedicated python shell (not shared with the other python buffers) to the current python buffer. To make this the default behavior (like the deprecated option elpy-dedicated-shells did), use the following snippet:

(add-hook 'elpy-mode-hook (lambda () (elpy-shell-toggle-dedicated-shell 1)))
M-x elpy-shell-set-local-shell

Attach the current python buffer to a specific python shell (whose name is asked with completion). You can use this function to have one python shell per project, with:

(add-hook 'elpy-mode-hook (lambda () (elpy-shell-set-local-shell (elpy-project-root))))
C-c C-k (elpy-shell-kill)

Kill the associated python shell.

C-c C-K (elpy-shell-kill-all)

Kill all active python shells.

Evaluating code fragments

Elpy provides commands to send the current Python statement (e), function definition (f), class definition (c), top-level statement (s), group of Python statements (g), cell (w), region (r), or buffer (b) to the Python shell for evaluation. These commands are bound to prefix C-c C-y, followed by the single character indicating what to send; e.g., C-c C-y e sends the Python statement at point.

Each of the commands to send code fragments to the shell has four variants, one for each combination of: whether or not the point should move after sending (“step”), and whether or not the Python shell should be focused after sending (“go”). Step is activated by C-, go by S-. For example:

C-c C-y e (elpy-shell-send-statement)

Send the current statement to the Python shell and keep point position. Here statement refers to the Python statement the point is on, including potentially nested statements. If point is on an if/elif/else clause send the entire if statement (with all its elif/else clauses). If point is on a decorated function, send the decorator as well.

C-c C-y C-e (elpy-shell-send-statement-and-step)

Send the current statement to the Python shell and move point to first subsequent statement.

Also bound to C-RET.

C-c C-y E (elpy-shell-send-statement-and-go)

Send the current statement to the Python shell, keeping point position, and switch focus to the Python shell buffer.

C-c C-y C-S-E (elpy-shell-send-statement-and-step-and-go)

Send the current statement to the Python shell, move point to first subsequent statement, and switch focus to the Python shell buffer.

Elpy provides support for sending multiple statements to the shell.

C-c C-y O (elpy-shell-send-group-and-step)

Send the current or next group of top-level statements to the Python shell and step. A sequence of top-level statements is a group if they are not separated by empty lines. Empty lines within each top-level statement are ignored.

If the point is within a statement, send the group around this statement. Otherwise, go to the top-level statement below point and send the group around this statement.

C-c C-y W (elpy-shell-send-codecell-and-step)

Send the current code cell to the Python shell and step. A code cell is a piece of code surrounded by special separator lines; see below. For example, you can insert two lines starting with ## to quickly send the code in-between.

elpy-shell-codecell-beginning-regexp (Customize Option)

Regular expression for matching a line indicating the beginning of a code cell. By default, ##.* is treated as a beginning of a code cell, as are the code cell beginnings in Python files exported from IPython or Jupyter notebooks (e.g., # <codecell> or # In[1]:).

elpy-shell-cell-boundary-regexp (Customize Option)

Regular expression for matching a line indicating the boundary of a cell (beginning or ending). By default, ##.* is treated as a cell boundary, as are the boundaries in Python files exported from IPython or Jupyter notebooks (e.g., # <markdowncell>, # In[1]:, or # Out[1]:).

Note that elpy-shell-codecell-beginning-regexp must also match the cell boundaries defined here.

The functions for sending the entire buffer have special support for avoiding accidental code execution, e.g.:

C-c C-y r (elpy-shell-send-region-or-buffer)

Send the the active region (if any) or the entire buffer (otherwise) to the Python shell and keep point position.

When sending the whole buffer, this command will also escape any uses of the if __name__ == '__main__' idiom, to prevent accidental execution of a script. If you want this to be evaluated, pass a prefix argument with C-u.

Also bound to C-c C-c.

elpy-shell-add-to-shell-history (Customize Option)

If t, Elpy will make the code sent available in the shell history. This allows to use comint-previous-input (C-up) in the python shell to get back the pieces of code sent by Elpy.

The list of remaining commands to send code fragments is:

C-c C-y s (elpy-shell-send-top-statement)
C-c C-y S (elpy-shell-send-top-statement-and-go)
C-c C-y f (elpy-shell-send-defun)
C-c C-y F (elpy-shell-send-defun-and-go)
C-c C-y c (elpy-shell-send-defclass)
C-c C-y C (elpy-shell-send-defclass-and-go)
C-c C-y o (elpy-shell-send-group)
C-c C-y O (elpy-shell-send-group-and-go)
C-c C-y w (elpy-shell-send-codecell)
C-c C-y W (elpy-shell-send-codecell-and-go)
C-c C-y R (elpy-shell-send-region-or-buffer-and-go)
C-c C-y b (elpy-shell-send-buffer)
C-c C-y B (elpy-shell-send-buffer-and-go)
C-c C-y C-s (elpy-shell-send-top-statement-and-step)
C-c C-y C-S-S (elpy-shell-send-top-statement-and-step-and-go)
C-c C-y C-f (elpy-shell-send-defun-and-step)
C-c C-y C-S-F (elpy-shell-send-defun-and-step-and-go)
C-c C-y C-c (elpy-shell-send-defclass-and-step)
C-c C-y C-S-C (elpy-shell-send-defclass-and-step-and-go)
C-c C-y C-S-O (elpy-shell-send-group-and-step-and-go)
C-c C-y C-W (elpy-shell-send-codecell-and-step-and-go)
C-c C-y C-r (elpy-shell-send-region-or-buffer-and-step)
C-c C-y C-S-R (elpy-shell-send-region-or-buffer-and-step-and-go)
C-c C-y C-b (elpy-shell-send-buffer-and-step)
C-c C-y C-S-B (elpy-shell-send-buffer-and-step-and-go)

Shell feedback

When package eval-sexp-fu is loaded and eval-sexp-fu-flash-mode is active, the statements sent to the shell are briefly flashed after running an evaluation command, thereby providing visual feedback.

elpy-shell-echo-input (Customize Option)

Whenever a code fragment is sent to the Python shell, Elpy prints it in the Python shell buffer (i.e., it looks as if it was actually typed into the shell). This behavior can be turned on and off via the custom variable elpy-shell-echo-input and further customized via elpy-shell-echo-input-cont-prompt (whether to show continuation prompts for multi-line inputs) and elpy-shell-echo-input-lines-head / elpy-shell-echo-input-lines-tail (how much to cut when input is long).

elpy-shell-echo-output (Customize Option)

Elpy shows the output produced by a code fragment sent to the shell in the echo area when the shell buffer is currently invisible. This behavior can be controlled via elpy-shell-echo-output (never, always, or only when shell invisible). Output echoing is particularly useful if the custom variable elpy-shell-display-buffer-after-send is set to nil (the default value). Then, no window is needed to display the shell (thereby saving screen real estate), but the outputs can still be seen in the echo area.

elpy-shell-display-buffer-after-send (Customize Option)

Whether to display the Python shell after sending something to it (default nil).

Syntax Checking

Whenever you save a file, Elpy will run a syntax check and highlight possible errors or warnings inline.

C-c C-n (elpy-flymake-next-error)
C-c C-p (elpy-flymake-previous-error)

You can navigate between any error messages with these keys. The current error will be shown in the minibuffer.

Elpy uses the built-in Flymake library to find syntax errors on the fly, so see there for more configuration options.

C-c C-v (elpy-check)

Alternatively, you can run a syntax check on the current file where the output is displayed in a new buffer, giving you an overview and allowing you to jump to the errors from there.

With a prefix argument, this will run the syntax check on all files in the current project.

python-check-command (Customize Option)

To change which command is used for syntax checks, you can customize this option. By default, Elpy uses the flake8 program, which you have to install separately. The elpy-config command will prompt you to do this if Elpy can’t find the program.

It is possible to create a single virtual env for the sole purpose of installing flake8 in there, and then simply link the command script to a directory inside your PATH, meaning you do not need to install the program in every virtual env separately.

Documentation

Elpy provides a single interface to documentation.

C-c C-d (elpy-doc)

When point is on a symbol, Elpy will try and find the documentation for that object, and display that. If it can’t find the documentation for whatever reason, it will try and look up the symbol at point in pydoc. If it’s not there, either, it will prompt the user for a string to look up in pydoc.

With a prefix argument, Elpy will skip all the guessing and just prompt the user for a string to look up in pydoc.

If the autodoc module is enabled (not by default) the documentation is automatically updated with the symbol at point or the currently selected company candidate.

elpy-autodoc-delay (Customize Option)

The idle delay in seconds until documentation is updated automatically.

Snippets

Elpy uses yasnippet to provide code templates that helps writing common pieces of code faster. You can access a template by typing a “template key” and hitting TAB to expand it. You may then be asked to fill some fields in the template, just hit TAB when you are done to proceed to the next field.

The sequel presents a list of templates provided by Elpy.

Special methods

Elpy provides a large range of templates for special class methods (__init__, __call__, __add__, …). To call them, simply type _ followed by the method name (for example _init) and hit TAB.

Other useful snippets

  • enc: Encoding statement
  • env: Hashbang statement
  • from: Import statement
  • pdb: Snippet to run pdb at the current script position
  • super: Super statement to call parent methods
  • def: Function definition
  • class: Class definition
  • defs: Class method definition

Folding

Elpy offers code folding by enhancing the builtin folding minor mode Hideshow.

When opening a python buffer, Elpy will indicate foldable things with an arrow in the left fringe. Clicking on an arrow will fold the corresponding code blocks. Folded code blocks can be unfolded by clicking on the button at the end of the line.

If you don’t want to use your mouse, you can achieve the same thing with the function

C-c @ C-c (elpy-folding-toggle-at-point)

Toggle folding for the thing at point, it can be a docstring, a comment or a code block.

The display of arrows in the fringe can be disable with the option

elpy-folding-fringe-indicators (Customize Option)

If elpy should display folding fringe indicators or not.

Elpy also provides some other useful features:

C-c @ C-b (elpy-folding-toggle-docstrings)

Toggle folding of all python docstrings.

C-c @ C-m (elpy-folding-toggle-comments)

Toggle folding of all comments.

C-c @ C-f (elpy-folding-hide-leafs)

Hide all code leafs, i.e. code blocks that do not contains any other blocks.

The classical keybindings for hideshow are also available, e.g.:

C-c @ C-a (hs-show-all)

Unfold everything.

(see Hideshow documentation for more information)

Debugging

Elpy provides an interface to pdb, the builtin Python debugger. Note that this interface is only available for Emacs 25 and above.

C-c C-u d (elpy-pdb-debug-buffer)

Run pdb on the current buffer. If no breakpoints has been set using elpy-pdb-toggle-breakpoint-at-point, the debugger will pause at the beginning of the buffer. Else, the debugger will pause at the first breakpoint. Once pdb is started, the pdb commands can be used to step through and look into the code evaluation.

With a prefix argument C-u, ignore the breakpoints and always pause at the beginning of the buffer.

C-c C-u b (elpy-pdb-toggle-breakpoint-at-point)

Add (or remove) a breakpoint on the current line. Elpy adds a red circle to the fringe to indicate the presence of a breakpoint. You can then use elpy-pdb-debug-buffer to start pdb and pause at each of the breakpoints.

With a prefix argument C-u, remove all the breakpoints.

C-c C-u p (elpy-pdb-break-at-point)

Run pdb on the current buffer and pause at the cursor position.

C-c C-u e (elpy-pdb-debug-last-exception)

Run post-mortem pdb on the last exception.

Testing

Testing is an important part of programming. Elpy provides a central interface to testing, which allows for a good workflow for tests.

Elpy’s test interface is built around Emacs’ compilation framework. Elpy will run test commands as a compilation job, with all the advantages this brings.

C-c C-t (elpy-test)

Start a test run. This uses the currently configured test runner to discover and run tests. If point is inside a test case, the test runner will run exactly that test case. Otherwise, or if a prefix argument is given, it will run all tests.

M-x elpy-set-test-runner

This changes the current test runner. Elpy supports the standard unittest discovery runner, the Django discovery runner, nose, green, py.test and Twisted trial. You can also write your own, as described in Writing Test Runners.

Note on Django runners: Elpy tries to find manage.py within your project structure. If it’s unable to find it, it falls back to django-admin.py. You must set the environment variable DJANGO_SETTINGS_MODULE accordingly.

This enables a good workflow. You write a test and use C-c C-t to watch it fail. You then go to your implementation file, for example using C-u C-c C-f, and make the test pass. You can use a key bound to recompile (I use <f5> for this) to just re-run that one test. Once that passes, you can use C-c C-t again to run all tests to make sure they all pass as well. Repeat.

For an even more automated way, you can use tdd.el, which will run your last compile command whenever you save a file.

Refactoring

C-c C-e (elpy-multiedit-python-symbol-at-point)

Edit all occurrences of the symbol at point at once. This will highlight all such occurrences, and editing one of them will edit all. This is an easy way to rename identifiers.

If the backend does not support finding occurrences (currently only Jedi does), or if a prefix argument is given, this will edit syntactic occurrences instead of semantic ones. This can match more occurrences than it should, so be careful. You can narrow the current buffer to the current function using C-x n d to restrict where this matches.

Finally, if there is a region active, Elpy will edit all occurrences of the text in the region.

C-c C-r f (elpy-format-code)

Format code using the available formatter.

If a region is selected, only that region is formatted. Otherwise current buffer is formatted.

elpy-formatter (Customize Option)

Allow to select the formatter you want to use amongst yapf , autopep8 and black.

yapf and autopep8 can be configured with style files placed in the project root directory (determined by elpy-project-root). black can be configured in the pyproject.toml file of your project.

Jedi refactoring

The following commands take advantage of Jedi refactoring possibilities. They all present a diff of the modifications before applying them, this allows to check the ongoing modifications and cancel some of them if needed.
C-c C-r r (elpy-refactor-rename)

Rename all occurences of the symbol at point (variable, function, class, …). If needed, rename occurences in other files as well.

C-c C-r v (elpy-refactor-extract-variable)

Move the selection to a new variable.

C-c C-r f (elpy-refactor-extract-function)

Move the selection to a new function.

C-c C-r i (elpy-refactor-inline)

Inline the variable at point. i.e. replace it with its defining expression.

Profiling

Elpy allows one to profile python scripts asynchronously using cProfile.

M-x elpy-profile-buffer-or-region

Send the current buffer or region to the profiler and display the result with elpy-profile-visualizer. The default visualizer is snakeviz, a browser-based graphical profile viewer that can be installed with pip install snakeviz. RunSnakeRun (Python-2 only GTK GUI) and pyprof2calltree (uses QCacheGrind or KCacheGrind for display) are supported alternatives and can be similarly installed with pip.

Django

Elpy has basic Django support such as parsing either manage.py or django-admin.py (If it does not find manage.py it falls back to django-admin.py) for command completion assistance. Can also start runserver automatically and you can give an ip address and port.

C-c C-x c (elpy-django-command)

Choose what command you’d like to run via django-admin.py or manage.py. Please note that for compatibility reasons, the shell command will use python (instead of ipython by default).

C-c C-x r (elpy-django-runserver)

Start the development server command, runserver. Default arguments are 127.0.0.1 for ip address and 8000 for port. These can be changed via elpy-django-server-ipaddr and elpy-django-server-port.