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Date: Thu, 16 Jan 2014 02:59:42 -0800 (PST)
From: Albert-Jan Roskam <fomcl@yahoo.com>
Subject: Re: Is it possible to get string from function?
To: python-list@python.org, Peter Otten <__peter__@web.de>
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Xref: csiph.com comp.lang.python:64073



--------------------------------------------
On Thu, 1/16/14, Peter Otten <__peter__@web.de> wrote:

 Subject: Re: Is it possible to get string from function?
 To: python-list@python.org
 Date: Thursday, January 16, 2014, 9:52 AM
=20
 Roy Smith wrote:
=20
 > I realize the subject line is kind of meaningless, so
 let me explain :-)
 >=20
 > I've got some unit tests that look like:
 >=20
 > class Foo(TestCase):
 >=A0=A0=A0def test_t1(self):
 >=A0 =A0=A0=A0RECEIPT =3D "some string"
 >=20
 >=A0=A0=A0def test_t2(self):
 >=A0 =A0=A0=A0RECEIPT =3D "some other string"
 >=20
 >=A0=A0=A0def test_t3(self):
 >=A0 =A0=A0=A0RECEIPT =3D "yet a third string"
 >=20
 > and so on.=A0 It's important that the strings be
 mutually unique.=A0 In the
 > example above, it's trivial to look at them and observe
 that they're all
 > different, but in real life, the strings are about 2500
 characters long,
 > hex-encoded.=A0 It even turns out that a couple of
 the strings are
 > identical in the first 1000 or so characters, so it's
 not trivial to do
 > by visual inspection.
 >=20
 > So, I figured I would write a meta-test, which used
 introspection to
 > find all the methods in the class, extract the strings
 from them (they
 > are all assigned to a variable named RECEIPT), and
 check to make sure
 > they're all different.
 >=20
 > Is it possible to do that?=A0 It is straight-forward
 using the inspect
 > module to discover the methods, but I don't see any way
 to find what
 > strings are assigned to a variable with a given
 name.=A0 Of course, that
 > assignment doesn't even happen until the function is
 executed, so
 > perhaps what I want just isn't possible?
 >=20
 > It turns out, I solved the problem with more mundane
 tools:
 >=20
 > grep 'RECEIPT =3D ' test.py | sort | uniq -c
 >=20
 > and I could have also solved the problem by putting all
 the strings in a
 > dict and having the functions pull them out of
 there.=A0 But, I'm still
 > interested in exploring if there is any way to do this
 with
 > introspection, as an academic exercise.
=20
 Instead of using introspection you could make it explicit
 with a decorator:
=20
 $ cat unique_receipt.py=20
 import functools
 import sys
 import unittest
=20
 _receipts =3D {}
 def unique_receipt(receipt):
 =A0 =A0 def deco(f):
 =A0 =A0 =A0 =A0 if receipt in _receipts:
 =A0 =A0 =A0 =A0 =A0 =A0 raise ValueError(
 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0
 "Duplicate receipt {!r} in \n=A0 =A0 {} and \n=A0
 =A0 {}".format(
 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0
 =A0 =A0 receipt, _receipts[receipt], f))
 =A0 =A0 =A0 =A0 _receipts[receipt] =3D f
 =A0 =A0 =A0 =A0 @functools.wraps(f)
 =A0 =A0 =A0 =A0 def g(self):
 =A0 =A0 =A0 =A0 =A0 =A0 return f(self,
 receipt)
 =A0 =A0 =A0 =A0 return g
 =A0 =A0 return deco
=20
 class Foo(unittest.TestCase):
 =A0 =A0 @unique_receipt("foo")
 =A0 =A0 def test_t1(self, RECEIPT):
 =A0 =A0 =A0 =A0 pass
=20
 =A0 =A0 @unique_receipt("bar")
 =A0 =A0 def test_t2(self, RECEIPT):
 =A0 =A0 =A0 =A0 pass
=20
 =A0 =A0 @unique_receipt("foo")
 =A0 =A0 def test_t3(self, RECEIPT):
 =A0 =A0 =A0 =A0 pass
=20
 if __name__ =3D=3D "__main__":
 =A0 =A0 unittest.main()
 $ python unique_receipt.py=20
 Traceback (most recent call last):
 =A0 File "unique_receipt.py", line 19, in <module>
 =A0 =A0 class Foo(unittest.TestCase):
 =A0 File "unique_receipt.py", line 28, in Foo
 =A0 =A0 @unique_receipt("foo")
 =A0 File "unique_receipt.py", line 11, in deco
 =A0 =A0 receipt, _receipts[receipt], f))
 ValueError: Duplicate receipt 'foo' in=20
 =A0 =A0 <function test_t1 at 0x7fc8714af5f0> and
=20
 =A0 =A0 <function test_t3 at 0x7fc8714af7d0>
=20

 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D> Very cool approach. Question, though=
: what would be wrong with the following approach:


import unittest

class Test(unittest.TestCase):

    receipts =3D {}

    def unique_value(self, k, v):
        assert Test.receipts.get(k) is None, "Duplicate: %s" % v
        Test.receipts[k] =3D v       =20

    def test_a(self):
        self.unique_value("large_value", "foo")

    def test_b(self):
        self.unique_value("large_value", "bar")  # oh no, a duplicate!=20

    def test_c(self):
        self.unique_value("another_large_value", "blah")
=09=09
unittest.main()