Skip to content
Projects
Groups
Snippets
Help
Loading...
Help
Support
Keyboard shortcuts
?
Submit feedback
Contribute to GitLab
Sign in / Register
Toggle navigation
C
cpython
Project overview
Project overview
Details
Activity
Releases
Repository
Repository
Files
Commits
Branches
Tags
Contributors
Graph
Compare
Issues
0
Issues
0
List
Boards
Labels
Milestones
Merge Requests
0
Merge Requests
0
Analytics
Analytics
Repository
Value Stream
Wiki
Wiki
Members
Members
Collapse sidebar
Close sidebar
Activity
Graph
Create a new issue
Commits
Issue Boards
Open sidebar
Kirill Smelkov
cpython
Commits
c48e26dc
Commit
c48e26dc
authored
Jul 31, 2018
by
INADA Naoki
Committed by
GitHub
Jul 31, 2018
Browse files
Options
Browse Files
Download
Email Patches
Plain Diff
bpo-27671: Update FAQ about why len is function (GH-8432)
parent
b229b072
Changes
1
Show whitespace changes
Inline
Side-by-side
Showing
1 changed file
with
19 additions
and
18 deletions
+19
-18
Doc/faq/design.rst
Doc/faq/design.rst
+19
-18
No files found.
Doc/faq/design.rst
View file @
c48e26dc
...
...
@@ -215,24 +215,25 @@ objects using the ``for`` statement. For example, :term:`file objects
Why does Python use methods for some functionality (e.g. list.index()) but functions for other (e.g. len(list))?
----------------------------------------------------------------------------------------------------------------
The major reason is history. Functions were used for those operations that were
generic for a group of types and which were intended to work even for objects
that didn't have methods at all (e.g. tuples). It is also convenient to have a
function that can readily be applied to an amorphous collection of objects when
you use the functional features of Python (``map()``, ``zip()`` et al).
In fact, implementing ``len()``, ``max()``, ``min()`` as a built-in function is
actually less code than implementing them as methods for each type. One can
quibble about individual cases but it's a part of Python, and it's too late to
make such fundamental changes now. The functions have to remain to avoid massive
code breakage.
.. XXX talk about protocols?
.. note::
For string operations, Python has moved from external functions (the
``string`` module) to methods. However, ``len()`` is still a function.
As Guido said:
(a) For some operations, prefix notation just reads better than
postfix -- prefix (and infix!) operations have a long tradition in
mathematics which likes notations where the visuals help the
mathematician thinking about a problem. Compare the easy with which we
rewrite a formula like x*(a+b) into x*a + x*b to the clumsiness of
doing the same thing using a raw OO notation.
(b) When I read code that says len(x) I *know* that it is asking for
the length of something. This tells me two things: the result is an
integer, and the argument is some kind of container. To the contrary,
when I read x.len(), I have to already know that x is some kind of
container implementing an interface or inheriting from a class that
has a standard len(). Witness the confusion we occasionally have when
a class that is not implementing a mapping has a get() or keys()
method, or something that isn't a file has a write() method.
-- https://mail.python.org/pipermail/python-3000/2006-November/004643.html
Why is join() a string method instead of a list or tuple method?
...
...
Write
Preview
Markdown
is supported
0%
Try again
or
attach a new file
Attach a file
Cancel
You are about to add
0
people
to the discussion. Proceed with caution.
Finish editing this message first!
Cancel
Please
register
or
sign in
to comment