mvdef 0.8.0

Package providing command line tools to move/copy function/classesand their associated import statements between files

mvdef

Package providing command line tools to move/copy Python functions/classes and their associated import statements between files.

Installation

To get the 4 mvdef tools on your command line, install from PyPi

pip install mvdef

All commands share identical usage syntax, but either move/copy the functions/classes indicated:

• cpdef
• mvcls
• cpcls

(Note that you may not mix and match these operations within a single call)

Recipes

Specifying what to move and where to move it to

mvdef is called on the command line with at the least an -m flag specifying the function to move (e.g. foo), the file it's in (e.g. src.py) and the file to move it to (which will be created if it doesn't exist).

mvdef -m foo src.py dst.py

Additionally, -i specifies a 'path' to move the function into, e.g. within a class Bar:

mvdef -m foo -i Bar src.py dst.py

Some points to note about these flags:

• The -m flag can be repeated for as many functions as you want to move
• The -i flag is optional for any/every -m flag (but must come immediately after)
  • Without -i, the function named in -m will go in the global namespace (i.e. unindented) at the end of the file
• Both the -m and -i paths can have parts separated by:
  • . to indicate the method of a class
  • : to indicate the inner function of a function
  • :: to indicate the inner class of a class
  • ::: to indicate the higher order class of a function
    • (i.e. a class inside a funcdef, which I was advised might also be known as "a regret")

Additionally:

• The -m/--mv flags can go anywhere but I find it more natural to place them first, so the command reads "move {this function} from {this file} to {this file}")
• If you move the last item out of a funcdef or class, mvdef will automatically repair it so it's still valid Python by replacing the excised lines with a pass statement

Still hungry? See the cookbook below!

Usage

Run mvdef -h to get this reminder:

usage: mvdef [-h] [-m MV] [-i INTO] [-v] [-b] [-d] src dst

Move function definitions and associated import statements from one file to another within a
library.

positional arguments:
  src
  dst

optional arguments:
  -h, --help            show this help message and exit
  -m MV, --mv MV
  -i INTO, --into INTO
  -v, --verbose
  -b, --backup
  -d, --dry-run

• For development flags not shown above (--debug, --show-tracebacks, --demo) see below

Cookbook

If you're curious to try this out but don't want to dive straight in, below are some more examples for the careful.

A cautious check before moving

mvdef -m myfunc src.py dst.py -vd

• -v is "verbose": print out the import statement edits to be made and functions to move
• -d is "dry run": don't edit any files, just prepare as if you were about to
  • It's not possible to run a dry run without a report, mvdef will tell you it has "nothing to do"

This is handy to check that there are no errors in the specified move, i.e. that the move will be possible (for example that you didn't make typos in any names), and will give a printout of what import statements will change in each file edited (if any).

A safeguarded move

mvdef -m myfunc src.py dst.py -vb

• -v: "verbose" (as above, print out import statement edits and funcdefs to move)
• -b: "backup", make backups (not overwriting prior ones, as .backup, then .backup0, etc)
  • src.py --> .src.py.backup
  • dst.py --> .dst.py.backup

A simple move with a specified target

mvdef -m foo -i Bar src.py dst.py

This moves the lines of the funcdef foo from src.py to the end of the classdef Bar (and note that this will indent the lines of foo by 4 spaces).

Moving methods between classes

mvdef -m A.__init__ -i B src.py dst.py

will move the method __init__ from the class A in src.py into the class B in dst.py

• Note that unlike the Unix tools mv and cp, the mvdef tools do not overwrite a function if it already exists, so if the class B already has an __init__ function it will simply end up with 2 __init__ functions, its original will not be overwritten.
• Additionally, the default position for newly moved (or copied) defs is at the end of the AST node (or the end of the namespace if no -i/--into node is specified), so in the case that the destination namespace ends up with duplicates, e.g. the B class with 2 __init__ functions, the newly moved one would "act last" i.e. it would take priority when instantiating the class, as of course the latest definition overwrites any earlier definition of the same ID.

Multiple moves

mvdef -m hello -i Bar.foo -m baz -i Bax src.py dst.py

will move:

• the funcdef hello from the global namespace of src.py into the method foo of the class Bar in dst.py (making it an inner function of the method)
• the funcdef baz from the global namespace of src.py into the class Bax in dst.py (making it a method of the class)

Coming soon

Paths to -mv/--mv and -i/--into will soon support:

• decorators: to indicate a particular version of funcdefs with identical names
  • e.g. for property decorators which have a @property and a @foo.setter variant
  • see #10
• wildcards: to avoid having to specify a full path to a particular function
  • e.g. -m **foo
  • see #28

Moving with imports: a simple case study

Consider the file hello.py:

from pprint import pprint

def hello():
    pprint("hi")

To move the hello funcdef to the blank file world.py, we run:

mvdef -m hello hello.py world.py -v

⇣

--------------RUNNING mvdef.cli⠶main()--------------
• Determining edit agenda for hello.py:
 ⇢ MOVE  ⇢ (import 0:0 on line 1) pprint ⇒ <pprint.pprint>
⇒ Functions moving from /home/ubuntu/stuff/simple_with_import_edit/hello.py: ['hello']
• Determining edit agenda for world.py:
 ⇢ TAKE  ⇢ (import 0:0 on line 1) pprint ⇒ <pprint.pprint>
⇒ Functions will move to /home/ubuntu/stuff/simple_with_import_edit/world.py
------------------COMPLETE--------------------------

New features

Check out the releases and changelogs in full on GitHub

Development flags

--debug

When you want to debug why something works or why it didn't work, change the mvdef -m ... command to python -im mvdef -m ... to gain an interactive shell after the command runs. If you supply --debug at the end of this command, the variable link will be populated with the FileLink instance which can be inspected and debugged (without need for pdb).

-show-tracebacks

By default, mvdef will curtail the stack trace when raising an error (as robust interfaces are more user-friendly).

To print the full stack trace, add the --show-tracebacks flag (and submit errors you find on GitHub).

--demo

To run a built-in demo, run mvdef --demo (equivalent to running the following within the package source):

mvdef -m pprint_dict mvdef/example/demo_program.py mvdef/example/new_file.py -vd

• The function pprint_dict is moved from the source file to the destination file, taking along import statements (or more precisely, taking individual aliases from import statements, which then form new import statements in the destination file). The top right of the image displays a report of the 'agenda' which mvdef follows, alias by alias, to carry out these changes.
• This demo can be reproduced by running python -im mvdef --demo from the main directory upon cloning this repository, and inspecting the source file (demo_program.py) and destination file (new_file.py) under mvdef/example/.
• This demo creates hidden .backup files, which can be used to 'reset' the demo by moving them back so as to overwrite the original files.

mvdef --demo will display a (dry run) demo of the output from moving a function from one file to another (in colour in the terminal, using ANSI codes):

--------------RUNNING mvdef.demo⠶main()--------------
{'foo': 1, 'bar': 2}
hello//human, welcome to spin.systems
✔ All tests pass
• Determining edit agenda for demo_program.py:
 ⇢ MOVE  ⇢ (import 0:0 on line 1) ft ⇒ <functools>
 ⇢ MOVE  ⇢ (import 1:0 on line 2) pprint ⇒ <pprint.pprint>
 ⇢ MOVE  ⇢ (import 1:1 on line 2) pformat ⇒ <pprint.pformat>
⇠  KEEP ⇠  (import 3:1 on line 4) pathsep ⇒ <os.path.sep>
⇠  KEEP ⇠  (import 2:0 on line 3) req ⇒ <urllib.request>
 ✘ LOSE ✘  (import 3:0 on line 4) bname ⇒ <os.path.basename>
 ✘ LOSE ✘  (import 3:2 on line 4) islink ⇒ <os.path.islink>
⇒ Functions moving from /home/louis/dev/mvdef/src/mvdef/example/demo_program.py: ['pprint_dict']
• Determining edit agenda for new_file.py:
 ⇢ TAKE  ⇢ (import 0:0 on line 1) ft ⇒ <functools>
 ⇢ TAKE  ⇢ (import 1:0 on line 2) pprint ⇒ <pprint.pprint>
 ⇢ TAKE  ⇢ (import 1:1 on line 2) pformat ⇒ <pprint.pformat>
⇒ Functions will move to /home/louis/dev/mvdef/src/mvdef/example/new_file.py
DRY RUN: No files have been modified, skipping tests.
------------------COMPLETE--------------------------

Motivation

My workflow typically involves a process of starting to work in one file, with one big function, and later breaking out that function into smaller functions once I've settled on the first draft of control flow organisation.

After 'breaking out' the code into multiple smaller functions in this way, it'll often be the case that some of the functions are thematically linked (e.g. they operate on the same type of variable or are connected in the workflow). In these cases, it's useful to move function definitions out of the main file, and into a module file together, then import their names back into the main file if or as needed.

• If I have two functions A and B, and my file calculates A() + B(), not only can I move A and B into some other module file mymodule, but I can put a wrapper function C in it too, and reduce the number of names I import

  def C():
      ans = A() + B()
      return ans
  

  both saving on the complexity in the main file, and giving 'more space' to focus on A, B and C separate from the complexity of what's going on in the main file (which in turn makes theme-focused tasks like documentation more straightforward).

The problem comes from then having to do the mental calculation (and often old fashioned searching for library-imported names within the file) of whether the functions I am trying to move out into another file rely on names that came from import statements, and if so, whether there are other functions which also rely on the same imported names. If I guess and get it wrong, I may then have to run the code multiple times and inspect the error message tracebacks until I figure out the full set, or else just reset it to where I was if things get particularly messy, in which case the time spent trying to move functions and import statements manually was wasted.

All of this motivates a library which can handle such operations for me, not just because it requires some thought to do manually so much as that it's a waste of development time, and what's more it interrupts the train of thought (increasingly so as the software gets more complex, with more functions and libraries to consider).

Software can scale to handle these higher levels of complexity no differently than it can handle a simple case, and I began writing this on the basis that "if I'm going to figure it out for this one instance, I may as well code it for any instance going forward".

TODO

• Back up src.py and dst.py, as src.py.backup and dst.py.backup in case it doesn't work
  • Function completed in src.backup⠶backup() with dry_run parameter, called in src.demo
  • I'd also like to add the option to rename functions, using a pattern or list to rename as
    • src.rename not yet implemented
• Optional: Define some test that should pass after the refactor, when src.py imports fn1, fn2, fn3 from dst.py
  • Tests defined for all functions in example.demo_program in example.test⠶test_report, called in __main__
    • Tests are checked and raise a RuntimeError if they fail at this stage (i.e. the whole process aborts before any files are modified or created)
  • If not, it would just be a matter of testing this manually (i.e. not necessary to define test to use tool, but suggested best practice)
• Enumerate all import statements in src.py (nodes in the AST of type ast.Import)
  • src.ast_util⠶annotate_imports returns this list, which gets assigned to imports in src.ast_util⠶parse_mv_funcs
• Enumerate all function definitions in src.py (nodes in the AST of type ast.FunctionDef)
  • ast⠶parse provides this as the .body nodes which are of type ast.FunctionDef.
    • This subset of AST nodes is assigned to defs in src.ast_util⠶ast_parse.
• Find the following subsets:
  • mvdefs: subset of all function definitions which are to be moved (fn1, fn2, fn3)
    • This subset is determined by cross-referencing the names of the defs (from previous step) against the mvdefs (list of functions to move, such as ["fn1", "fn2", "fn3"]), in the dedicated function src.ast_util⠶get_def_names, then returned by src.ast_tools⠶ parse_mv_funcs as a list, assigned to mvdefs in src.ast_util⠶ast_parse.
  • nonmvdefs: subset of all function definitions not to be moved (not in mvdefs)
    • This subset is determined by negative cross-ref. to names of the defs against the mvdefs (such as ["fn4", "fn5", "fn6"]), again using src.ast_util⠶get_def_names, then returned by src.ast_util⠶parse_mv_funcs as a list, assigned to nonmvdefs in src.ast_util⠶ast_parse.
  • mv_imports: Import statements used only by the functions in mvdefs
  • nonmv_imports: Import statements used only by the functions in nonmvdefs
  • mutual_imports: Import statements used by both functions in mvdefs and nonmvdefs
  • nondef_imports: Import statements not used by any function
    • Note that these may no longer be in use, but this can only be confirmed by checking outside of function definitions too.
    • Potentially add this feature later, for now just report which imports aren't used.
• Handle the 3 types of imported names:
  • Move the import statements in mv_imports (received as "take")
  • Keep the import statements in nonmvdef_imports
  • Copy the import statements in mutual_imports (received as "echo")
• ...and also:
  • Handle moving one import name from an import statement importing multiple names (i.e. where you can't simply copy the line)
  • Handle multi-line imports (i.e. where you can't simply find the names on one line)
  • ...and remove unused import statements (neither in/outside any function definitions)
• ...and only then move the function definitions in mvdefs across
• If tests were defined in step 2, check that these tests run
  • For the demo, the tests are checked (by running test_report a 2nd time) after src.demo⠶run_demo has returned a parsed version of the source and destination files (which will only matter once the parameter nochange is set to False in run_demo, allowing it to propagate through the call to src.demo⠶parse_example into a call to src.ast_util⠶ast_parse(..., edit=True) and ultimately carry out in-place editing of the source and/or destination file/s as required).
  • If they fail, ask to restore the backup and give the altered src/dst .py files .py.mvdef_fix suffixes (i.e. always permit the user to exit gracefully with no further changes to files rather than forcing them to)