Summary

Introduces four different forms using a repeat keyword. It also demonstrates how to use a callback parameters.

repeat as a keyword

Let’s begin with an example.

> python -m ideas -a repeat --show
Ideas Console version 0.0.38. [Python version: 3.9.10]

ideas> repeat 3:
   ...     print('Hello')
   ...
===========Transformed============
for _9e4a6946f8d44ffca90dc9475537d39a in range( 3):
    print('Hello')

-----------------------------
Hello
Hello
Hello

ideas>

As you can see, repeat n, where n is an integer, is converted into a for loop, with a randomly named variable, guaranteed not to have a name used for another object in the program. This works well in practice.

However, suppose we wish to do some repeatable tests, ensuring that the variable names are always the same for all tests: we can do this using a ‘callback parameter’. This is a parameter that is given to the add_hook function used to create the import hook. add_hook must use Python dict to pass all required callback parameters to create_hook, so that they can be passed back to the function used to transform the code.

Here’s a second example using it.

>>> from ideas.examples import repeat
>>> from ideas.console import start
>>> from ideas.session import config
>>> config.show_changes = True
>>> repeat.add_hook(predictable_names=True)
<IdeasMetaFinder object for ideas.examples.repeat>
>>> start()
Ideas Console version 0.0.38. [Python version: 3.9.10]

ideas> repeat 3:
   ...     print('Hello')
   ...
===========Transformed============
for _1 in range( 3):
    print('Hello')

-----------------------------
Hello
Hello
Hello

ideas>

As you can see, the name of the for loop variable, _1, is much simpler … and predictable.

You will need to have a look at the code for repeat.py to fully understand how to use such callback parameters in your own import hooks.

Adds repeat as a keyword to write loops. The four constructs supported are:

repeat n:
    # code

repeat while condition:
    # code

repeat until condition:
    # code

repeat forever:
    # code

For example:

repeat 3:
    a = 2
    repeat a*a:
        pass

is equivalent to:

for unique_variable_name_1 in range(3):
    a = 2
    for unique_variable_name_2 in range(a*a):
        pass

exception ideas.examples.repeat.RepeatSyntaxError

Currently, only raised when a repeat statement has a missing colon.

ideas.examples.repeat.add_hook(predictable_names=False, **_kwargs)

Creates and adds the import hook in sys.meta_path.

If predictable_names is set to True, a callback parameter passed to the source transformation function will be used to create variable loops with predictable names.

ideas.examples.repeat.transform_source(source, callback_params=None, **_kwargs)

This function is called by the import hook loader and is used as a wrapper for the function where the real transformation is performed.

It can use an optional parameter, callback_params, which is a dict that can contain a key, "predictable_names", to indicate that variables created as loop counters should take a predictable form.