to be None and then run as if an identity string had
been provided.
Raymond Hettinger
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e-up very well (with each Python
implementation having its own limits on how far you can push this
idiom).
Raymond
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xecute the operation
itself.
Executive summary: Python's for-loops are both elegant and fast. It
is a mistake to habitually avoid them.
Raymond
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ON001370
http://docs.python.org/lib/module-collections.html
Raymond
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c = *args # three elements, no problem
f(*xrange(100)) # too much data, not scalable, bad idea
Whenever you get the urge to write something like the latter, then take
it as cue to be passing iterators instead of unpacking giant tuples.
Raymond
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[Vivek Chaudhary]
> Is it possible to set an environment variable in python script whose
> value is retained even after the script exits.
There is an indirect approach:
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/159462
Raymond
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[Brian Quinlan]
> I'm doing to judge the solutions based on execution speed. It sucks but
> that is the easiest important consideration to objectively measure.
. . .
> I'm always looking for feedback, so let me know what you think or if you
> have any ideas for future problems.
I'm curious about
[Will McGugan]
> I need a collection class that behaves like a dictionary but when it
> reaches 'n' items it discards the oldest item so that the length never
> goes above 'n'. (Its for caching search results)
import collections
class Cache(dict):
def __init__(self, n, *args, **kwds):
n attribute of f
. . .
Raymond
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> > [sj]
> >> Thus, random access is an O(1) operation while insertion/deletion is an
> >> O(n) operation.
[Raymond Hettinger]
> > Yes.
[Heikki Orsila aka host.invalid]
> Unfortunately no. Check Terry Reeds answer. Random access is O(1),
> insertion/deletion
> > [Andy]
> >>How can you unit test nested functions?
[Raymond Hettinger]
> > For whitebox testing, you could make an inner function visible by
> > binding it to the enclosing function's attribute namespace.
> >
> >def f(x):
> >
[Raymond Hettinger]
> >class Cache(dict):
> >def __init__(self, n, *args, **kwds):
> >self.n = n
> >self.queue = collections.deque()
> >dict.__init__(self, *args, **kwds)
[Bengt Richter]
> Minor comment: There is a potential name co
er
languages.
In contrast, the existing behavior of zip() is quite useful. It allows
some of the input sequences to be infinite:
zip(itertools.count(1), open('myfile.txt'))
Raymond
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arked the trail; don't ignore the signs unless you really know where
you're going.
Raymond
"... and soon you'll feel right as rain." -- from The Matrix
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> This is the seventh summary written by the python-dev summary cabal of
> Steve Bethard, Tim Lesher, and Tony Meyer.
Thanks guys. The work is excellent and appreciated.
Raymond
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Once() is
trivially coded using a global or class variable to restrict running to
a single occasion. If that seems unpleasant, then encapsulate the
logic in a subclass of TestCase, in a decorator, or in a metaclass.
If you want better, try py lib's py.test module which is both more
mini
lly poll resources and shut them
off if they are not in use -- loosely translated as having a security
guard turn-off any coffee-pots that were left on by frazzled
programmers as they leave at odd hours of the night.
Raymond
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eet your needs:
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/305268
Raymond
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ly asking so I can cleanup any craziness in my code before I try
> and release pyiw (the Python bindings for Wireless Networking in Linux).
> I really want it to be as clean as possible before showing anyone
> else. :)
I'm sure your users will appreciate the devotion to quality.
Raymond
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> Googling for information on securing Python in a "sandbox" seems
> indicate that there are some built in features, but they aren't really
> trustworthy. Is that correct?
>
> For my purposes, I really just want to let users run in a sandbox, with
> access to only the language, manipuate a few publ
robes
to find a global value).
When the extra value was added, it likely resized the table four-fold
and redistributed the hash values into fewer consecutive positions.
Raymond
P.S. To analyze it further, start with something like this:
>>> len(set(hash('dummy%d' %i) & 31 fo
Claudio Grondi wrote:
> Is there any deeper reason I don't understand
> explaining why does min(A,B) behave different
> for classes than for lists?
Yes, the sort order for lists is determined by their contents. With
your example, the lists have identical contents, so min() returns the
first minim
is not very useful in your case. It
works a bit like this:
def __cmp__(self, other):
return cmp(id(self), id(other))
This is mildly useful as it allows distinct
objects to have an ordering relation.
Raymond
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[Raymond Hettinger]
> > With respect to
> > distribution, it should be noted that string hash values are decidely
> > non-random and your variable names likely congested consecutive spaces
> > in a nearly full table (resulting in seven times as many search probes
&g
See PEP 322 for discussion and examples:
http://www.python.org/peps/pep-0322.html
Raymond
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John Machin wrote:
> Looks like arrays are NOW (2.4.1) pickleable but not unpickleable
Please file a bug report and assign to me.
Raymond Hettinger
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ame tuple vs scalar issue.
> So, take this as a bug report if the behavior is not intended and
> as a feature request if the current behaviour is the intended
> one ;)
Feel free to post a SF report. If Barry wants to alter the behavior,
it is easy enough to do:
try:
retur
or.'
It is intended. The behavior is defined as above (a series of indexed
lookups).
BTW, the usual ways to deal with this are to:
1. iterating from the right using: for item in reversed(data)
2. making a copy of the original list before iterating
3. creating a new result list: data = [x for x in data if 'DEL' not in
x]
Raymond
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Sep 15 2005, 00:51:34) [MSC v.1200 32 bit (Intel)] on
win32
Type "copyright", "credits" or "license()" for more information.
>>> def f():
return 2+3
>>> import dis
>>> dis.dis(f)
2 0 LOAD_CONST 3 (5)
3 RETURN_VALUE
Raymond
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end up with [0,1,2,3,2,4,5].
>>> import itertools
>>> [k for k, v in itertools.groupby(lst)]
[0, 1, 2, 3, 2, 4, 5]
Raymond Hettinger
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for elem in s:
bag[elem] = bag.get(elem, 0) + 1
print [elem for elem, count in bag.iteritems() if count>1]
Raymond Hettinger
P.S. Extra credit problem: make the itertools solution output values in the
order seen.
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ribly opposed to the idea. I just
find the case for it to be somewhat weak. Also, I'm not sure it warrants the
effort, the code clutter, or introducing issues like having a semantic
difference between the result of frozenset() and the result of frozenset([]).
Raymond Hettinger
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ods, both set() and frozenset() share the same
underlying code and data structure. In this respect, they differ from list()
and tuple() which have no shared code and has two substantially different
data structures.
Raymond Hettinger
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If you're
living in a pre 2.2 world without iterators and generators, you're really
missing out.
Raymond Hettinger
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[Nick Coghlan]
> > Hmm, it might be nice if there was a UserList.ListMixin that was the
> > counterpart to UserDict.DictMixin
[Steven Bethard]
> I've thought this occasionally too. One of the tricky issues though is
> that often you'd like to define __getitem__ for single items and have
> ListM
en('corpus.uniq'):
print >> out, '%.14f %s' % (random(), line),
>>> out.close()
sort corpus.decorated | cut -c 18- > corpus.randomized
Raymond Hettinger
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list.sort(lambda a, b: cmp((a[i], a[j], a[k]), (b[i], b[j], b[k])))
In Py2.4, the key= option offers an alternative to cmp which is simpler and
faster:
def sort_by_key(list, i, j, k):
list.sort(key = lambda a : (a[i], a[j], a[k]))
Raymond Hettinger
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nd how to combine them. The time and skill seems to rise exponentially with
the number of tools in the module. So, it would be a mistake to add a few
obscure, rarely used tools because that would impact the usability of the
existing toolset.
'nuff said, mister whatever happened to batteries i
u need that to be flattened one level, it would have been better to do all
the splits at once:
# split on tabs, spaces, and newlines
r = map(float, open('namefile').read().split())
Generalizing the two results, it may be fair to say that the desire to flatten
is a code smell
else:
iterstack.pop() # only remove iterator when it is exhausted
Raymond Hettinger
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ee also iterator,
sequence, and generator.
Raymond Hettinger
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. So,
consider reversing ';>' to '>;'.
Raymond Hettinger
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not fail. Knowing that fact is the key to a complete and deep
understanding of monglation ;-)
Raymond Hettinger
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nd how to integrate them with other Python code. IMO,
most of the recipes are more useful in this capacity than as immediate solutions
to particular problems.
Raymond Hettinger
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n the standard library =), is a better
> solution than duplicating the code (or the function call) to translate,
> reverse, and format the string.
While the use of groupby() is brilliant, I prefer the previous version as a
demonstration of beautiful, general purpose, plain Python code running at
full-speed.
Raymond Hettinger
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map() is only for situations where the data is already in tuple form.
If it inputs are already distinct, imap() is the preferred form.
FWIW, the answer was already in the docs (itertools recipes):
def dotproduct(vec1, vec2):
return sum(imap(operator.mul, vec1, vec2))
Raymond Hettinger
;,'l'])
> L=[s1,s2,s3,s4,s5]
> --- > cleaned-up list should contain s1, s3, s5
This should do the trick:
result = []
for s1 in L:
for s2 in result:
if s1 <= s2:
break
else:
result.append(s1)
print result
Raymond Hettinger
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"Kent Johnson" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> Raymond Hettinger wrote:
> > [EMAIL PROTECTED]
> >
> >>I have many set objects some of which can contain same group of object
> >>while others can be subset of the other.
if key not in d:
d.key = {subkey:value}
else:
d[key][subkey] = value
Raymond Hettinger
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>
> How do you define "largest" ? ;-)
> I guess you could sum(map(len, setlist)) as a measure, but what if that makes
> a tie between two setlists (as I think it could, in general)?
With multiple outputs satisfying the constraints, I would suspect that there is
something wrong with the original spec (not as a stand-alone problem, but as
component of a real application).
Raymond Hettinger
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ey:value}
else:
d[key][subkey] = value
Raymond
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> psyco - Armin Rigo
This is platform specific.
Raymond
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[Jeff Epler]
> Maybe something for sets like 'appendlist' ('unionset'?)
I do not follow. Can you provide a pure python equivalent?
Raymond
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to True or False:
any(x >= 42 for x in data)
If you wanted an identify function, that simplifies to just:
any(data)
Raymond Hettinger
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ce and provide a better designed tool rather than just
a name change.
> Just my 2 Eurocents,
I raise you by a ruble and a pound ;-)
Raymond Hettinger
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to the key should be emphasised more. Hence valadd or such?
How about countkey() or tabulate()?
Raymond Hettinger
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full statement: d.setdefault(k,
[]).append(v).
My thought is that setdefault() is rarely used by itself. Instead, it is
typically part of a longer sentence whose intent and meaning is to accumulate or
build-up. That meaning is not well expressed by the current idiom.
Raymond Hettinger
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a little less elegant:
False not in (x >= 42 for x in data)
Raymond Hettinger
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y while retaining the original value. IOW, your
re-write is incorrect:
>>> L = ['the', 'quick', 'brownish', 'toad']
>>> max(L, key=len)
'brownish'
>>> max(len(x) for x in L)
8
Remain calm. Keep the fait
27;t mind
writing out the plain Python for this one if it only comes up once in a blue
moon.
Raymond
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contain strong
cues that remind you of addition and of building a list.
For the first, how about addup():
d = {}
for word in text.split():
d.addup(word)
Raymond
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[Ivan Van Laningham]
> What about adding another method, "setincrement()"?
. . .
> Not that there's any real utility in that.
That was a short lived suggestion ;-)
Also, it would entail storing an extra value in the dictionary header. That
alone would be a killer.
ility.
BTW, there is no need to make the same post three times.
Raymond
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atomic as this expression can get. Any other steps,
added verbiage, new types, extra arguments, or whatnot are an unnecessary waste
of brain cells.
Raymond Hettinger
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((0, (1, 0, 1), 1)))
> '1.01E+3'
> >>>
>
> how do you make the 2nd example print 1010?
The quantize method will convert to any desired exponent (zero in your example):
>>> d = (Decimal((0, (1, 0, 1), 1)))
>>> d
Decimal("1.01E+3")
>>> d.quantize(Decimal(1))
Decimal("1010")
Raymond Hettinger
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nt?
Yes:
>>> set((x,round(y)) for x,y in a) & set((x,round(y)) for x,y in b)
set([(123, 8.0), (123, 2.0), (123, 1.0)])
> I'm using python 2.3.
>>> from sets import Set as set
>>> set([(x,round(y)) for x,y in a]) & set([(x,round(y)) for x,y in b])
set([(123, 8.0), (123, 2.0), (123, 1.0)])
Raymond Hettinger
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double quotes? For making changes to Python code, I
> would also like to avoid changing text in comments, either the '#' or
> '""" ... """' kind.
The source for the tokenize module covers all these bases.
Raymond Hettinger
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omps and genexps.
If you want to go the extra distance, itertools.izip() can offer a performance
boost and better memory utilization than zip(). It can be used almost anywhere
as long as the app doesn't demand a real list.
Raymond Hettinger
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ist comprehensions got a nice 60% boost on my
machine:
C:\py24\Lib>\python23\python timeit.py -r9 "[i for i in xrange(1000)]"
100 loops, best of 9: 1.11 msec per loop
C:\py24\Lib>\python24\python timeit.py -r9 "[i for i in xrange(1000)]"
1000 loops, best of 9: 417
;None' only just became a constant in 2.4.
>
> I don't know if 'True' and 'False' are in line for similar treatment (there
are
> obvious backwards compatibility issues in doing so).
It is unlike to before Py3.0. Making them constants would break the reams
,y in zip(a,b))
0.635497577901 sum(imap(mul, a, b))
0.85894416601 sum(map(mul, a, b))
C:\pydev>python timedot.py 10
2.19490353509 sum(a[i]*b[i] for i in xrange(len(a)))
2.01773998894 sum(x*y for x,y in izip(a,b))
2.44932533231 sum(x*y for x,y in zip(a,b))
1.24698871922 sum(imap(mul, a, b))
1.
all in comparison.
Raymond Hettinger
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leton instance of None. That will
occur even if you've mucked with None entry in the globals dictionary.
Bytecode for eval() doesn't go through the bytecode optimizer so its dictionary
lookup is retained (producing the effect in your example).
To have made None a literal constant would
a,b))
1.62 sec:sum(x*y for x,y in zip(a,b))
0.75 sec:sum(imap(mul, a, b))
1.04 sec:sum(map(mul, a, b))
Raymond Hettinger
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posting present only toy
examples -- real use cases have not yet emerged. If some do emerge, I
suspect that each problem will have a better solution (using existing
tools) than the one being proposed. If so, then adopting the proposal
will have the negative effect of leading folks away from the corre
le)
... rows = range(len(data))
... for col in xrange(len(data[0])):
... args = [data[row][col] for rows in rows]
... yield f(*args)
Raymond Hettinger
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)*Decimal('85')-Decimal('.1234')/Decimal('81.6')
--> Decimal("0.01659274509803921568627450980")
1.0/7
--> 0.14285714285714285
Decimal('1.0')/Decimal('7')
--> Decimal("0.1428571428571428571428571429")
"""
Raymond Hettinger
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[Jack Diederich]
> > itertools to iter transition, huh? I slipped that one in, I mentioned
> > it to Raymond at PyCon and he didn't flinch. It would be nice not to
> > have to sprinkle 'import itertools as it' in code. iter could also
> > become a ty
> > [Julian Hernandez Gomez]
> >> is there a "easy way" to make eval() convert all floating
> >> numbers to Decimal objects and return a Decimal?
[Raymond Hettinger]
> > from decimal import Decimal
> > import re
> >
> > number =
> &
nalty just to create the possibility of weak referencing.
While the design decision is unlikely to change, the docs could certainly be
improved. A doc patch would be welcome.
FWIW, the work-arounds are to weak-reference instances of UserString or to
create a custom class with a has-a relationship in
;, binascii.unhexlify(_))[0]
3.1415927410125732
Writing to a file is accomplished with the open() function and the file.write()
method:
f = open('mydata.hex', 'w')
f.write('40490fdb')
f.close()
Raymond Hettinger
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inner. When you're done, consider posting the result as an ASPN
cookbook recipe.
Raymond Hettinger
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mments, competing recipes, and Alex/Anna's
editing). The cookbook is its own microcosm of open source.
Raymond Hettinger
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[David Bear]
> I'm looking for an 'easy' way to have the last item in a list returned.
Try mylist.pop() or mylist[-1].
Raymond Hettinger
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, elem1, elem2--]
[--tuple header, elem0 ]
In contrast, ints and floats floats have no problem because they are always the
same size:
[--int header, int value--]
Raymond Hettinger
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your best bet is to eliminate the initial linear search which
is likely consuming most of the clock cycles.
Also, I noticed that the code does not reference self. Accordingly, it is a
good candidate for being a staticmethod or standalone function.
Raymond Hettinger
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test is based on a proven
model and the code is mature.
unittest module updates come up in distinct releases, often months or years
apart. py.test is subject to constant update by subversion. Personally, I like
the continuous updates, but it could be unsettling if you're depending
ite a pure python equivalent for
list:
def lyst(s):
it = iter(s)
result = []
try:
while 1:
result.append(it.next())
except StopIteration:# guess who trapped StopIter
return result
Raymond Hettinger
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e, some will adopt another, and the world will
> become fragmented.
Worry is a natural thing for someone with "panix" in their email address ;-)
FWIW, the evolution of py.test is to also work seemlessly with existing tests
from the unittest module.
the world diversifies, the worl
f.lower())
def __eq__(self, other):
return self.lower() == other.lower()
>>> d = {}
>>> d[S('ThE')] = 'quick'
>>> d[S('the')]
'quick'
>>> d
{'ThE': 'quick'}
Raymond Hettinger
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)).
For the performance minded, there could also be a control for dictionary
speed/space efficiency:
t = TrickyDict()
t.maxkeydensity = 40 # resize whenever the dictionary is more than 40%
full
Taken together, these six attributes/methods could cover many wished for
features for the 10% of the cases where a regular dictionary doesn't provide the
best solution.
Raymond
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Right.
attrgetter gets but does not call.
If unicode isn't an issue, then the lambda can be removed:
>>> [''.join(g) for k, g in groupby(' test ing ', str.isspace)]
[' ', 'test', ' ', 'ing', ' ']
Raymond Hettinger
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tage is the clarity of the resulting code and the
avoidance of continous reinvention of workarounds.
Separating tool features into a basic and an advanced version is common solution
to managing option/customization complexity.
Raymond
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2 in (x for x in xrange(5) if show(x)<4 or stop())
> 0 1 2
> True
> >>> 7 in (x for x in xrange(5) if show(x)<4 or stop())
> 0 1 2 3 4
> False
>
> BTW I notice that this also nicely shortcuts when the 2 is found.
That's a fact.
Raymond
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#x27;m a little puzzled why folks so often consider this
> particularly "heavy".
unittest never felt heavy to me until I used py.test. Only then do you realize
how much boilerplate is needed with unittest. Also, the whole py.test approach
has a much simpler object model.
BTW, th
rt people: enough to make me want to take a
> closer look at it to see what the fuss is about. :-)
FWIW, py.test scales nicely. Also, it takes less time to try
it out or read the docs than discuss it to death on a newsgroup.
The learning curve is minimal.
Raymond Hettinger
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[Peter Hansen]
> This is pretty, but I *want* my tests to be contained
> in separate functions or methods.
In py.test, those would read:
def test1():
assert a == b
def test2():
raises(Error, func, args)
Enclosing classes are optional.
Raymond
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self.assertEqual over and
over again. The generative tests are especially nice.
Until you've exercised both packages, you haven't helped the OP
whose original request was: "Is there anybody out there who has
used both packages and can give a comparative review?"
Raymond
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my bet is that they will live on.
The more likely change is that in Py3.0 list comps will no longer expose the
loop variable outside the loop.
Raymond Hettinger
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[Steven Bethard]
> and I often find myself alternating
> between the two when I can't decide which one seems more Pythonic.
Both are pythonic.
Use a genexp when you need a generator
and use a listcomp when you need a list.
Raymond Hettinger
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