Názor k článku Perličky: úvod do referencí od anonym - Samozřejmě funguje i toto: def process_code(code): ...

def process_code(code):
    indentLevel = 0
    indentedRows = []
    for row in (r.strip() for r in code.split('\n')):
        if (not row):
            continue
        if row == 'BEGIN':
            indentLevel += 1
        elif row == 'END':
            indentLevel -= 1
        else:
            indentedRows.append(indentLevel * ' ' + row)
    return '\n'.join(indentedRows)

exec process_code('''
print "Kaslu na level"

for a in xrange(3):
BEGIN
for b in xrange(4):
BEGIN
        print a * b
END
END

print "Vse v poradku"
''')