A good eval for discord.py

eval.py

import ast
import discord

from discord.ext import commands


def insert_returns(body):
    # insert return stmt if the last expression is a expression statement
    if isinstance(body[-1], ast.Expr):
        body[-1] = ast.Return(body[-1].value)
        ast.fix_missing_locations(body[-1])

    # for if statements, we insert returns into the body and the orelse
    if isinstance(body[-1], ast.If):
        insert_returns(body[-1].body)
        insert_returns(body[-1].orelse)

    # for with blocks, again we insert returns into the body
    if isinstance(body[-1], ast.With):
        insert_returns(body[-1].body)


@commands.command()
async def eval_fn(ctx, *, cmd):
    """Evaluates input.

    Input is interpreted as newline seperated statements.
    If the last statement is an expression, that is the return value.

    Usable globals:
      - `bot`: the bot instance
      - `discord`: the discord module
      - `commands`: the discord.ext.commands module
      - `ctx`: the invokation context
      - `__import__`: the builtin `__import__` function

    Such that `>eval 1 + 1` gives `2` as the result.

    The following invokation will cause the bot to send the text '9'
    to the channel of invokation and return '3' as the result of evaluating

    >eval ```
    a = 1 + 2
    b = a * 2
    await ctx.send(a + b)
    a
    ```
    """
    fn_name = "_eval_expr"

    cmd = cmd.strip("` ")

    # add a layer of indentation
    cmd = "\n".join(f"    {i}" for i in cmd.splitlines())

    # wrap in async def body
    body = f"async def {fn_name}():\n{cmd}"

    parsed = ast.parse(body)
    body = parsed.body[0].body

    insert_returns(body)

    env = {
        'bot': ctx.bot,
        'discord': discord,
        'commands': commands,
        'ctx': ctx,
        '__import__': __import__
    }
    exec(compile(parsed, filename="<ast>", mode="exec"), env)

    result = (await eval(f"{fn_name}()", env))
    await ctx.send(result)