BPython Lives!!!

2006-04-02 01:56

In January, I suggested it would be trivial to write a preprocessor that would accept a version of python which delimited blocks with braces instead of indentation.

Ok, almost, I suggested #{ and #} as delimiters.

Well, I had a few minutes free today, and here it is, a functional BPython->Python compiler, so to speak.

Here's the kind of imput it takes (notice how it's not indented at all:

def factorial(n):
#{
if n==1:
#{
return 1
#}
else:
#{
return n*factorial(n-1)
#}
#}

for x in range(1,10):
#{
print x,"!=",factorial(x)
#}

And it produces this (I am not happy with the indenting of the comments, but who cares):

def factorial(n):
  #{
  if n==1:
    #{
    return 1
  #}
  else:
    #{
    return n*factorial(n-1)
  #}
#}

for x in range(1,10):
  #{
  print x,"!=",factorial(x)
#}

As you can see, this is both a legal Python and a legal BPython program ;-)

It has some problems, like not working when you use a line like this:

#{ x=1

But hey, it is python with braces.

Here's the code. I predicted 30 lines. It's 34. And it's 99% a ripoff of Ka Ping Yee's regurgitate.py which you can find all around the web.

#!/usr/bin/env python
import tokenize, sys
program = []
lastrow, lastcol = 1, 0
lastline = ''
indlevel=0
def rebuild(type, token, (startrow, startcol), (endrow, endcol), line):
    global lastrow, lastcol, lastline, program,indlevel
    if type==52 and token.startswith ("#{"):
            type=5
            indlevel+=1
    if type==52 and token.startswith ("#}"):
            type=6
            indlevel-=1
    line="  "*indlevel+line.lstrip()
    startcol+=indlevel*2
    endcol+=indlevel*2
    # Deal with the bits between tokens.
    if lastrow == startrow == endrow:            # ordinary token
        program.append(line[lastcol:startcol])
    elif lastrow != startrow:                    # backslash continuation
        program.append(lastline[lastcol:] + line[:startcol])
    elif startrow != endrow:                     # multi-line string
        program.append(lastline[lastcol:startcol])
    # Append the token itself.
    program.append(token)
    # Save some information for the next time around.
    if token and token[-1] == '\n':
        lastrow, lastcol = endrow+1, 0           # start on next line
    else:
        lastrow, lastcol = endrow, endcol        # remember last position
    lastline = line                              # remember last line
tokenize.tokenize(sys.stdin.readline, rebuild)
for piece in program: sys.stdout.write(piece)

So, all of you who dislike python because of the lack of braces and the significant whitespace:

BPython has no significant whitespace, and braces are mandatory.

Enjoy coding!

Ralsina.Me — Roberto Alsina's website