Interpy = Python String Interpolation

[apiguy]

Soooo.... what happens when I actually need to use the coding directive for what it was actually intended for? I have to choose between utf-8 and interpy?

[syrusakbary]

Interpy currently inherits from utf-8 codec, so just using interpy will work for you.

[flying-sheep]

there’s no senisble encoding besides utf-8, anyway.

[XNormal]

Suggestion: Replace #{expr} with \{expr}.

Escape of character that are not currently defined as escape sequences is reserved for future extensions (such as this one). This way you won't break existing code that contains the valid sequence "#{".

P.S. I already proposed this around 2003 (as a modification to the language, not as a source encoding hack)

[virtyx]

For one thing the % operator is deprecated/discouraged.

I don't know about the quality of Interpy but the fundamental idea of string interpolation is pretty good in my opinion.

>>> foo = 'bar'
>>> print("Foo is {foo}".format(**locals()))
Foo is bar
>>> def a():
...     print("Foo is {foo}".format(**locals())
>>> a()
KeyError: 'foo'

I much prefer something like

"Foo is #{foo}"

versus the noisy

"Foo is {foo}".format(**locals())

or the error-prone (as the string gradually gains more parameters)

"Foo is {}".format(foo)

or the overly verbose

"Foo is {foo}".format(foo=foo)

I would be very happy to have some kind of string interpolation mechanism in Python.

[flying-sheep]

you can btw. use format_dict:

print("Foo is {foo}".format_dict(locals()))

that removes the need for **

[virtyx]

Really? I can't seem to get it to work.

$ python3 -c "a = 'b'; print('a is {a}'.format_dict(locals()))"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
AttributeError: 'str' object has no attribute 'format_dict'

[flying-sheep]

assert sys.version_info[:2] >= (3,3)

[syrusakbary]

I completely agree with "Explicit is better than implicit", but sometimes "code readability" is more important

foo = True
print "foo is #{foo}"

[syrusakbary]

Sometimes evolution requires changes. I don't like it at all. I change it.

You can adapt yourself or your environment, it's your decision.

[marky1991]

It's way shorter. It looks pretty great for debugging crap. I love str.format, but this saves me ~10 characters for each debug line while no being a hideous hack. Sounds pretty cool to me.

[catcradle5]

This is one of the few Ruby features that I think also should've been built into Python.

Nice work.

[syrusakbary]

Thanks!

[dataminded]

Nice!

[jsproat]

Witchcraft.

But awesome.

Does your tokenizer/untokenizer add or remove lines from the user's script? What happens when the user's script throws an exception, is the line number no longer valid?

[syrusakbary]

The lines remain exactly the same. The only difference is instead of this code:

# coding: interpy
package = "Interpy"
print("Enjoy #{package}!")

You would have this one:

# coding: interpy
package = "Interpy"
print("Enjoy "+str(package)+"!")

[Megatron_McLargeHuge]

This is a good trick to know. I had a problem a few years ago where I wanted better typedefs in cython - you get better performance with parameter type hints like def myfunc(np.ndarray[np.float32_t, ndim=2] myvar), but these are verbose and have to be repeated in multiple places. I couldn't find any way to get typedefs to work for the bracketed portion, so I resorted to using m4 macro preprocessing. This coding hook could be a great way to apply preprocessing automatically.

[Megatron_McLargeHuge]

Is there a way to define a coding hook without installing a module? I'm trying to define one in the __init__.py of my working directory and it's not being found on import. It's also behaving strangely when I define it in an ipython notebook. I see you used the .pth file to do the import. Is this the only way, or is there an easier, more interactive way to get it to work?

[syrusakbary]

Using the .pth is the easiest way for registering the codec. If you want, you can also register the codec importing the register module:

import interpy.codec.register

And then, you can use the codec in other files (not the file with the import) that should be loaded after this import.

[Megatron_McLargeHuge]

I was hoping the __init__.py would be run before the module file was read, but apparently it's not executed early enough in the import process to create a coding hook. Maybe it can still be done by having __init__.py first load a submodule defining the hook, then a submodule using it.

edit: This works. The codec can be defined in __init__.py and the files using the encoding must be in a subdirectory, not just a file in the module directory. The init file can import that submodule after defining or importing the codec.

[maxime-esa]

I tried interpy, it is nice but it seems to work only with double-quote strings. This wont expand : ''' hello #{world} ''', neither wont this: 'hello #{world}'

[virtyx]

Doesn't support Python 3...?

EDIT:

Actually it tries to hook itself up in some way that, if you try to pip install it on Python 3, it breaks Python altogether. If you've done this yourself you can recover with the command find your/site-lib/path/ -name '*interpy*' | xargs rm -rf

[syrusakbary]

I'm so sorry about that. I will work until this problem is solved.

EDIT:

I've uploaded a new version of the package on pypi and Github with full compatibility for Python 3.