BUG: check if a collections.Sequence on printing

[jreback]

http://stackoverflow.com/questions/15769706/converting-a-list-in-a-dict-to-a-series/15770083?noredirect=1#comment22416395_15770083

[ghost]

related #3000, #3005 , it's a general pattern, ABCs did not see heavy use when pandas
was in it's formative stage and so it's type-directed behaviour is too strict.

[jreback]

yep....also need to accept this in the constructors (as well as output-formatters)

maybe should have a function to basically do the test isinstance(obj,list)
(which sometimes needs a tuple sometimes not), so maybe modify
_is_sequence_like a bit

[ghost]

the opt-in register() mechanism of the ABCs is pretty useful, just need
to be careful of sharp corners: strings are sequences of-course, also #2978

[jreback]

actually this is a bit more complicated, the problem is that a Timestamp is a sequence as well! (and we often have to do some checking to avoid treating it like a list); np.scalar I think should be redefined a bit (there is a routine somewhere in the cython code to do scalar testing in any event...should be fixed/consolidated as well)

[ghost]

what?! how is Timestamp a sequence?

In [39]: t=Timestamp("2000-1-1")

In [40]: t[0]
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-40-d0a24a012877> in <module>()
----> 1 t[0]

TypeError: 'Timestamp' object does not support indexing

In [41]: list(t)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-41-f57fd3c9bd0b> in <module>()
----> 1 list(t)

TypeError: 'Timestamp' object is not iterable

In [42]: import collections

In [43]: isinstance(t,collections.Sequence)
Out[43]: False

[jreback]

sorry...meant that it isn't a scalar (though we treat it like one)

In [4]: np.isscalar(1)
Out[4]: True

In [5]: np.isscalar(pd.Timestamp('20010101'))
Out[5]: False

[jtratner]

@jreback maybe this is silly, but why is the way that it prints actually wrong? Is there another example where this would matter? [clearly, I'm going through earlier bug reports]

[jreback]

no the issue here is this

is you have a list of lists then the DataFrame constructor works fine

but if its a list-of-sequencers that are not lists but act like lists (eg collections.Sequence) then it doesn't work

this used to work when we used np.asarray but for various reasons the conversions are now a bit more 'manual'

so this is actually pretty easy to just accept a collections.Sequence in the constructors

[WillAyd]

Closed due to age and ambiguity. If there is a reproducible example for issue feel free to reopen