Is arr len the preferred way to get the length of an array in Python

Question

In Python  is the following the only way to get the number of elements   arr   len       If so  why the strange syntax

User · Answer

The way you take a length of anything for which that makes sense (a list, dictionary, tuple, string, ...) is to call len on it.

l = [1,2,3,4]
s = 'abcde'
len(l) #returns 4
len(s) #returns 5

The reason for the "strange" syntax is that internally python translates len(object) into object.__len__(). This applies to any object. So, if you are defining some class and it makes sense for it to have a length, just define a __len__() method on it and then one can call len on those instances.

User · Answer

Python uses duck typing  it doesn t care about what an object is  as long as it has the appropriate interface for the situation at hand  When you call the built-in function len   on an object  you are actually calling its internal   len   method  A custom object can implement this interface and len   will return the answer  even if the object is not conceptually a sequence   For a complete list of interfaces  have a look here  http   docs python org reference datamodel html basic-customization

User · Answer

my list    1 2 3 4 5  len my list    5   The same works for tuples   my tuple    1 2 3 4 5  len my tuple    5   And strings  which are really just arrays of characters   my string    hello world  len my string    11   It was intentionally done this way so that lists  tuples and other container types or iterables didn t all need to explicitly implement a public  length   method  instead you can just check the len   of anything that implements the  magic    len     method   Sure  this may seem redundant  but length checking implementations can vary considerably  even within the same language  It s not uncommon to see one collection type use a  length   method while another type uses a  length property  while yet another uses  count    Having a language-level keyword unifies the entry point for all these types  So even objects you may not consider to be lists of elements could still be length-checked   This includes strings  queues  trees  etc   The functional nature of len   also lends itself well to functional styles of programming   lengths   map len  list of containers

User · Answer

you can use len arr   as suggested in previous answers to get the length of the array  In case you want the dimensions of a 2D array you could use arr shape returns height and width

User · Answer

len list name  function takes  list as a parameter and it calls list s   len     function

User · Answer

The preferred way to get the length of any python object is to pass it as an argument to the len function   Internally  python will then try to call the special   len   method of the object that was passed

User · Answer

Just use len arr     gt  gt  gt  import array  gt  gt  gt  arr   array array  i    gt  gt  gt  arr append  2    gt  gt  gt  arr   len     1  gt  gt  gt  len arr  1

User · Answer

Python suggests users use len   instead of   len     for consistency  just like other guys said  However  There re some other benefits   For some built-in types like list  str  bytearray and so on  the Cython implementation of len   takes a shortcut  It directly returns the ob size in a C structure  which is faster than calling   len       If you are interested in such details  you could read the book called  Fluent Python  by Luciano Ramalho  There re many interesting details in it  and may help you understand Python more deeply

[python] Is arr.len() the preferred way to get the length of an array in Python?

Examples related to python

Examples related to arrays

Examples related to methods

[python] Is arr.__len__() the preferred way to get the length of an array in Python?

Examples related to python

Examples related to arrays

Examples related to methods

[python] Is arr.len() the preferred way to get the length of an array in Python?