@BT: I suspect at least part of the reason for __len__ vs. .length() is that all names that begin and end with double-underscores (dunders) are: 1) Reserved for language use, and 2) Allow the language to bypass normal lookup rules (e.g. the method can be looked up directly on the instance's class w/o checking if the instance has shadowed it with an attribute of the same name).

Nov 11, 2009 · Besides len you can also use operator.length_hint (requires Python 3.4+). For a normal list both are equivalent, but length_hint makes it possible to get the length of a list-iterator, which could be useful in certain circumstances:

Dec 5, 2014 · I need to get the number of elements from node data['result'][0]['run']. It should be 3, but I can't find how to do it in Python. It should be 3, but I can't find how to do it in Python. python

Mar 29, 2017 · Python maps len(obj) onto obj.__len__. X.shape returns a tuple, which does have a len - which is the number of dimensions, X.ndim . X.shape[i] selects the ith dimension (a straight forward application of tuple indexing).

Jun 30, 2016 · Find length of 2D array Python. Ask Question Asked 12 years, 11 months ago. Modified 15 days ago.

Since the dimensions of a numpy array is stored as the shape attribute, getattr() can also be used. arr = np.arange(8).reshape(2,2,2) getattr(arr, 'shape') # (2, 2, 2) It's useful if you need to get it along with a dynamic list of other properties. An example could be

Jun 29, 2016 · However, there are in fact 10 elements in this 2D array. In the case of multi-dimensional arrays, len() gives you the length of the first dimension of the array i.e. import numpy as np len(a) == np.shape(a)[0] To get the number of elements in a multi-dimensional array of arbitrary shape: import numpy as np size = 1 for dim in np.shape(a): size ...

Mar 27, 2015 · The idiom used for this in python is len(obj), not obj.len() >>> v = 'ffff' >>> msg = bytearray(v.decode('hex')) >>> len(msg) 2 If you are creating your own class that should be able to report its length, implement the magic method __len__(self) , which will be called when the built-in function len() is called and passed an instance of your class.

Jul 8, 2013 · There is no general function that does what you ask, not least because Python itself does not define a matrix/array class. You certainly can write your own function which operates on iterable objects like lists and tuples if you are prepared to make assumptions, or write assertions, as to the uniformity of the list.

Aug 22, 2017 · jinja2's builtin filters are documented here; and specifically, as you've already found, length (and its synonym count) is documented to: Return the number of items of a sequence or mapping. So, again as you've found, {{products|count}} (or equivalently {{products|length}}) in your template will give the "number of products" ("length of list")