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I often copy things from my terminal to other places (like Discord), and to make my workflow even easier I decided to use the IPython API to make an extension that has two magic functions pickle and clip.

clip can copy the contents of a line (or cell). It can copy both, the input line or the output line.
pickle takes in a variable as an argument and pickles its contents and copies it to your clipboard, it can also unpickle your clipboard's content and load it into a variable or print it.

I've heard that unpickling unknown data can be dangerous but I'm not sure if there is anything I can do about that, other than assume that the user trusts the data he or she is unpickling. (If there are other alternatives please let me know).

Are there any improvements that I could apply to my code? Like making the docstrings/error messages more understandable or patching a bug that I have not spotted, or rewriting something specific.

I'm kind of concerned about the user trying to unpickle a large object, such as a pandas data frame (I was helping someone with a pandas question and told him to pickle the data frame and send it, I didn't feel any noticeable delay as I unpickled the file, but the data frame was small anyways).

I also don't know how I could create tests for magic functions in case I add any extra features or patches in the future.

Any recommendations and constructive feedback are welcome. Thank you for taking the time to read this.

import sys
from argparse import ArgumentTypeError
from ast import literal_eval
from keyword import iskeyword
from pickle import dumps as p_dumps
from pickle import loads as p_loads

import IPython.core.magic_arguments as magic_args
from IPython.core.magic import line_magic, Magics, magics_class
from pyperclip import copy as pycopy
from pyperclip import paste as pypaste


def valid_identifier(s: str):
    if not s.isidentifier() or iskeyword(s):
        raise ArgumentTypeError(f'{s} is not a valid identifier.')
    return s


def valid_line_num(s: str):
    valid_conditions = (
        s.isdigit(),
        s in '_ __ ___ _i _ii _iii'.split(),
        s.startswith('_') and s[1:].isdigit(),
        s.startswith('_i') and s[1:].isdigit()
    )
    if not any(valid_conditions):
        raise ArgumentTypeError(f'{s} is not a valid line number or a valid ipython cache variable (eg. `_` or `_i3`)')
    return s


@magics_class
class IPythonClipboard(Magics):
    @line_magic
    @magic_args.magic_arguments()
    @magic_args.argument('line_number',
                         default='_',
                         type=valid_line_num,
                         nargs='?',
                         help='The line number to copy the contents from'
                         )
    def clip(self, line: str = ''):
        """Copies an input or output line to the clipboard.
        `_i7` copies the  input from line 7
        `_7`  copies the output from line 7
        `7`   copies the output from line 7"""
        args = magic_args.parse_argstring(self.clip, line)
        line_num: str = args.line_number
        if line_num.isdigit():
            line_num = f'_{line_num}'
        ip = self.shell
        content: str = str(ip.user_ns.get(line_num, ''))
        pycopy(content)

    @line_magic
    @magic_args.magic_arguments()
    @magic_args.argument('--output', '-o',
                         type=valid_identifier,
                         nargs=1,
                         help='The variable to store the output to.')
    @magic_args.argument('var',
                         type=valid_identifier,
                         nargs='?',
                         help='The variable to pickle.')
    def pickle(self, line: str = ''):
        """
        Pickles a variable and copies it to the clipboard or un-pickles clipboard contents and prints or stores it.

        `%pickle` unpickle clipboard and print
        `%pickle v` pickle variable `v` and store in clipboard
        `%pickle _` pickle last line's output and store in clipboard
        `%pickle -o my_var` unpickle clipboard contents and store in `my_var`"""
        ip = self.shell
        args = magic_args.parse_argstring(self.pickle, line)
        if bool(args.output) and bool(args.var):
            msg = (
                'Incorrect usage, you can either pickle a variable, or unpickle, but not both at the same time.' '\n'
                '\n' f'`%pickle {args.var}` to pickle the contents of `{args.var}` and send them to your clipboard'
                '\n' f'`%pickle -o {args.output[0]}` to unpickle clipboard contents and send them to `{args.output[0]}`'
                '\n' f'`%pickle` to unpickle your clipboard contents and print'
            )
            ip.write_err(msg)
            return None

        if not line or args.output:  # user wants to unpickle from clipboard
            content: str = pypaste()
            possible_errors = (not content.startswith('b') and content[1] != content[-1],  # must be like b'...'
                               not content  # clipboard is empty
                               )
            if any(possible_errors):  # clipboard doesn't have a valid pickle string
                sys.stderr.write(r"Your clipboard doesn't have a bytes-like string (ie. b'\x80\x03N.')")
                return None

            if args.output:  # user wants to unpickle into a variable
                ip.user_ns[args.output[0]] = p_loads(literal_eval(content))

            else:  # user wants to unpickle and print
                sys.stdout.write(str(p_loads(literal_eval(content))))

        else:  # user wants to pickle a var
            pycopy(str(p_dumps(ip.user_ns.get(args.var))))


def load_ipython_extension(ipython):
    ipython.register_magics(IPythonClipboard)
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Valid line numbers

This is a mix of too-clever, not-very-efficient and not-informative-enough:

valid_conditions = (
    s.isdigit(),
    s in '_ __ ___ _i _ii _iii'.split(),
    s.startswith('_') and s[1:].isdigit(),
    s.startswith('_i') and s[1:].isdigit()
)
if not any(valid_conditions):
    raise ArgumentTypeError(f'{s} is not a valid line number or a valid ipython cache variable (eg. `_` or `_i3`)')
return s

It really needs to be exploded out to the various error conditions. Also, the fourth condition is likely incorrect because it will never be true; you probably meant [2:]. An example:

if s in {'_', '__', '___', '_i', '_ii', '_iii'} or s.isdigit():
    return s

match = re.match(r'_i?(.*)$', s)
if match is None:
    raise ArgumentTypeError(f'{s} is not a valid line number or a valid ipython cache variable (eg. `_` or `_i3`)')

if match[1].isdigit():
    return s

raise ArgumentTypeError(f'{s} has a valid prefix but {match[1]} is not a valid integer')

Similarly, this:

        possible_errors = (not content.startswith('b') and content[1] != content[-1],  # must be like b'...'
                           not content  # clipboard is empty
                           )
        if any(possible_errors):

should actually care that a single or double quote is used, and have separated error messages for mismatched quotes vs. missing 'b'. Don't handwave at your users - tell them exactly what went wrong.

Separated newlines

This:

        msg = (
            'Incorrect...time.' '\n'
            '\n' f'...

is odd. Why not just include the newlines in the same string?

        msg = (
            'Incorrect...time.\n\n'
            f'...
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  • \$\begingroup\$ I would also like to know why you chose to use a set in your example, instead of a tuple or a list. \$\endgroup\$ – Kato Jun 20 '20 at 6:45

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