I have mentioned before on this list that I am engaged in source
translation of a largeish Python prgram - 14KLOC - to Go. I found the
automated AST-based translation tools already available unsatisfactory;
they don't produce a quality of Go code I would consider maintainable. So
I wrote my own using crude, old-school regexp-bashing.
This turned out to be surprisingly effective. The following is from the
manual page:
* Opens Python block scopes with { and closes them with }.
* Changes docstrings to comments.
* Changes comments from #-led to //-led
* Translates Python boolean constants True, False to Go true, false
* Translates Python "in range" to Go ":= range", You will need to fix
up the comma and range clauses by hand.
* Maps Python single-quote literals to Go double-quote literals.
* Translates Python logical connectives and or not to Go && || !.
* Changes Python None to Go nil.
* Changes "def " at the left margin to "func ".
* Common cases of various Python string library methods - capitalize(),
count(), endswith(), find(), join(), lower(), lstrip(), rfind(), replace(),
rstrip(), split(), startswith(), split(), upper() - are translated to Go
string library calls.
* Some common Python standard library calls, notably from os and
os.filepath, are translated into Go equivalents. The result is not
guaranteed to be perfectly correct; a Python call that throws a signal on
failure may map into a Go function with an error return. But it will always
be a step in the right direction, and the Go compiler will respond with
indicative error messages.
* The append() method of Python is translated to a call to Go's append
intrinsic.
* Python's "del foo[bar]" is translated to Go "delete(foo, bar)". Note that
this can false-match on a list del with a numeric key; this
will throw a compilation error in Go and you can hand-fix it.
* Trailing line-continuation backslashes are removed.
* Python r-prefix string literals become Go backtick literals
* Python try/finally/catch become pseudo-statements with delimited block
scopes. You will need to fix these up by hand.
* Single-line % expressions with a string-literal left hand and either
tuple or single-variable right hands are translated into fmt.Sprintf
calls. You will need to translate %-cookies by hand; %r -> %v or %q is the
usual trouble spot.
* Changes multiline strings to backtick literals. You'll need to fix up
backslash escapes and %-cookies yourself.
* Many, but not necessarily all, cases where Go ":=" assignment can replace
a plain "=" assignment in Python are translated.
This doesn't do a complete job, of course. But it takes a lot of the pain
out of hand-translation, and it does preserve comments and structure.
Probably the automated block scope closing is the biggest single win;
that's a tedious, fiddly job by hand and mistakes are all too easy.
Future releases will translate a larger subset of Python standard library
calls.
The repository is at https://gitlab.com/esr/pytogo and the project home
page at http://www.catb.org/esr/pytogo/
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