command-reading

Script to get the last value out of a stack of Python commands. For example,


>>> from readcommands import *
>>> s = '''a = 'Catch'
... b = 22
... c = "Heller"'''
>>> lastValue(s)
'Heller'
>>> s = '''mynum = 100
... mynum + 10'''
>>> lastValue(s)
110


The script:


r"""
lastValue should return the last value assigned or otherwise
referred to in a stack of Python commands.

>>> lastValue('a=1')
1
>>> lastValue('a = 1\nb = 2')
2
>>> lastValue('beast = "cow"\nx = 22\nbeast')
'cow'
>>> lastValue('f=4.0\ni=7\ntarget=f')
4.0
>>> lastValue('f=4.0\ni=7\ntarget=f', types_of_interest=(int,))
7
"""

import unittest, doctest

def items_of_interest(dct, types_of_interest):
return [(k, v) for (k, v) in dct.items() if isinstance(v, types_of_interest)]

def recordingexec(arg, types_of_interest = (int, basestring)):
cmdbuf = []
lastlocals = []
for line in arg.strip().splitlines():
cmdbuf.append(line)
try:
oldlocals = items_of_interest(locals(), types_of_interest)
exec('\n'.join(cmdbuf))
newlocals = [itm for itm in
items_of_interest(locals(), types_of_interest)
if itm not in oldlocals]
if newlocals:
lastlocals = newlocals
lastcmd = '\n'.join(cmdbuf)
cmdbuf = []
except SyntaxError, e:
if not (('unexpected EOF while parsing' in str(e) or
('EOL while scanning') in str(e) )):
raise
return (lastcmd, dict(lastlocals))

def lastValue(s, types_of_interest=(basestring, int, float)):
s = s.strip()
if not s:
return None
exec(s)
(lastcmd, lastlocals) = recordingexec(s, types_of_interest)
try:
return eval(lastcmd)
except SyntaxError, e:
if 'invalid syntax' not in str(e):
raise
if len(lastlocals) > 1:
raise ValueError, "Multiple assignments - couldn't determine which one"
return eval(lastlocals.keys()[0])

class RecordingExecTestSuite(unittest.TestCase):
def testSimpleAssignments(self):
(lastcmd, lastlocals) = recordingexec('''
a = 1
b = "cow"
c = 3''')
self.assertEqual(lastcmd, 'c = 3')
self.assertEqual(lastlocals, {'c': 3})
def testIgnoreObj(self):
(lastcmd, lastlocals) = recordingexec('''
a = 1
b = 2
uts = unittest.TestSuite()
''', (unittest.TestSuite))
self.assertEqual(lastcmd, 'uts = unittest.TestSuite()')
self.assertEqual(lastlocals.keys(), ['uts'])
def testExecutableLastLine(self):
(lastcmd, lastlocals) = recordingexec('''
a = 1
print "hi mom"''')
self.assertEqual(lastcmd, 'print "hi mom"')
self.assertEqual(lastlocals, {'a': 1})
def testEvalLastLine(self):
(lastcmd, lastlocals) = recordingexec('''
a = 1
a''')
self.assertEqual(lastcmd, 'a')
self.assertEqual(lastlocals, {'a': 1})

class LastValueTestSuite(unittest.TestCase):
def testSimpleAssignments(self):
lv = lastValue('''
a = 1
b = "cow"
c = 3''')
self.assertEqual(lv, 3)
def testSimpleAssignments(self):
lv = lastValue('''
a = 1
b = "cow"
c = 3
b''')
self.assertEqual(lv, 'cow')
def testMultiAssignFail(self):
self.assertRaises(ValueError, lastValue, '''
a = 1
(b, c) = (2, 3)''')
def testEmpty(self):
lv = lastValue('')
self.assertEqual(lv, None)

if __name__ == '__main__':
#unittest.main()
doctest.testmod()