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py2star

Converts python files to starlark files

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Setup

python -m venv venv
source venv/bin/activate
python setup.py install

Run

cd src/py2star
python cli.py larkify ~/src/pycryptodome/lib/Crypto/SelfTest/PublicKey/test_RSA.py > test_RSA.star
python cli.py tests test_RSA.star >> test_RSA.star

Differences with Python

The list of differences between Starlark and Python are documented at https://bazel.build site:

• Differences with Python
• More differences documented as a Work In Progress in this Github issue

Some High-level Differences

• Global variables are immutable.
• for statements are not allowed at the top-level. Use them within functions instead.
• if statements are not allowed at the top-level. However, if expressions can be used: first = data[0] if len(data) > 0 else None.
• Deterministic order for iterating through Dictionaries.
• Recursion is not allowed.
• Modifying a collection during iteration is an error.
• Except for equality tests, comparison operators <, <=, >=, >, etc. are not defined across value types. In short: 5 < 'foo' will throw an error and 5 == "5" will return False.
• In tuples, a trailing comma is valid only when the tuple is between parentheses, e.g. write (1,) instead of 1,.
• Dictionary literals cannot have duplicated keys. For example, this is an error: {"a": 4, "b": 7, "a": 1}.
• Strings are represented with double-quotes (e.g. when you call repr).
• Strings aren't iterable (WORKAROUND: use .elems() to iterate over it.)

The following Python features are attempted to be automatically converted:

• most builtin functions, most methods.
• set types (WORKAROUND: use sets.star instead)
• [ ]implicit string concatenation (use explicit + operator).
• Chained comparisons (e.g. 1 < x < 5)`.
• class (see larky.struct function).
• import (see load statement).
• while.
• generators and generator expressions.
• is and is not (use == and != instead, respectively).
• raise (see fail for fatal errors).
• try, except, finally. (see fail for fatal errors).
• yield.
• global, nonlocal.

Automatic Conversion

• py2star.fixes.fix_declass -- de-classes and de-indents a class

So, it goes from:

class Foo(object):
    def bar(self):
        return "baz"

To:

def bar(self):
    return "baz"