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@beala /argy.py
Created Aug 11, 2012

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What would you like to do?
A command line argument parser using generators and co-routines.
"""
Inspired by:
http://eli.thegreenplace.net/2009/08/29/co-routines-as-an-alternative-to-state-machines/
"""
def parse_args(target):
"""A generator that parses a stream of arguments one character at a time.
As soon as a flag, or flag value pair ("-a" or "-a value") is processed
the pair is sent off as a tuple to the 'target' generator.
The parser can handle escape characters, and double and single quoting
of values:
-flag value
--a-flag value
-one flag --two flag
-quotes "Some \" text"
-quotes 'Some \' text'
-escaped-spaces here\ are\ some\ spaces
Use by sending characters one at a time:
p = parse_args()
p.next()
p.send('-')
p.send('a')
p.send(' ')
p.send('-')
# Sends ('-a', '') to target.
Sending the last " -" tricks the parser into sending the last flag
value pair, by making it think you're starting a new flag arg pair.
"""
# Grab the first char of the input.
char = (yield)
while True:
# Init the name and value pair. These will contain the name of the
# flag (so "a" for -a) and the value, if there is one (so, "val" for
# -a val).
name = ""
value = ""
while True:
# This loop iterates once per: name or value. Also iterates thru
# spaces that aren't a part of a name or value.
if char == " ":
# Skip spaces.
char = (yield)
elif char == "-":
if name != "":
break
# Start processing new option flag.
while char == "-":
# Skip hyphens at beginning.
char = (yield)
while char != " ":
# Keep grabbing characters until we get to a space.
name += char
char = (yield)
elif char.isalnum():
# Start processing unquoted value.
value += char
char = (yield)
while char.isalnum():
# Keep grabbing characters until we get to a non-alpha
# numeric character signalling the value is over.
value += char
char = (yield)
while char == "\\":
# If the escape character is countered, just add
# the the character following it to the value.
value += (yield)
char = (yield)
# Grab next char for next iteration.
char = (yield)
# At this point, we should have a flag and value pair.
# Breaking will get us to target.send
break
elif char in ["\'", "\""]:
# Process quoted value.
# Remember the quote character.
quote = char
char = (yield)
while char != quote:
# Keep grabbing chars until we get to the matching quote.
value += char
char = (yield)
while char == "\\":
# Handle the escape character.
value += (yield)
char = (yield)
# Forwad past the matching quote.
char = (yield)
# Grab next char for next iteration.
char = (yield)
break
# Send the name, value pair to the receiver.
target.send( (name, value) )
def target():
"""Simple target for the arg parser that just prints out each pair.
"""
while True:
print repr((yield))
# Functions for creating and initializing generators.
def make_target():
t = target()
t.next()
return t
def make_parser(*args, **kwargs):
p = parse_args(*args, **kwargs)
p.next()
return p
if __name__=="__main__":
tests= [
"-a",
"--a-long-arg",
"-name1 value",
"-name2 'single quote'",
'-name3 "double quote"',
r"-name4 spaces\ using\ escape\ chars",
"-name5 'escaping in quotes: \''",
"-one arg --two-args val",
]
parser = make_parser(make_target())
for test in tests:
print "Testing: %s" % repr(test)
for c in test:
parser.send(c)
parser.send(" ")
parser.send("-")
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