python: how to identify if a variable is an array or a scalar

>>> import collections.abc
>>> isinstance([0, 10, 20, 30], collections.abc.Sequence)
True
>>> isinstance(50, collections.abc.Sequence)
False

note: isinstance also supports a tuple of classes, check type(x) in (..., ...) should be avoided and is unnecessary.

You may also wanna check not isinstance(x, (str, unicode))

As noted by @2080 and also here this won’t work for numpy arrays. eg.

>>> import collections.abc
>>> import numpy as np
>>> isinstance((1, 2, 3), collections.abc.Sequence)
True
>>> isinstance(np.array([1, 2, 3]), collections.abc.Sequence)
False

In which case you may try the answer from @jpaddison3:

>>> hasattr(np.array([1, 2, 3]), "__len__")
True
>>> hasattr([1, 2, 3], "__len__")
True
>>> hasattr((1, 2, 3), "__len__")
True

However as noted here, this is not perfect either, and will incorrectly (at least according to me) classify dictionaries as sequences whereas isinstance with collections.abc.Sequence classifies correctly:

>>> hasattr({"a": 1}, "__len__")
True
>>> from numpy.distutils.misc_util import is_sequence
>>> is_sequence({"a": 1})
True
>>> isinstance({"a": 1}, collections.abc.Sequence)
False

You could customise your solution to something like this, add more types to isinstance depending on your needs:

>>> isinstance(np.array([1, 2, 3]), (collections.abc.Sequence, np.ndarray))
True
>>> isinstance([1, 2, 3], (collections.abc.Sequence, np.ndarray))
True