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Ned Grossy
Courses Plus Student 3,292 PointsHow add own functionality to standard Python function ?
Hello everyone.
I have watched a lecture about how to remove items from a list and decided to add own keyword optional argument to remove all instances of specified argument from a list.
For example:
a = [1, 2, 3, 1] a.remove(1) # a = [2, 3, 1]
I want: a = [1, 2, 3, 1] a.remove(1, all = True) # a = [2, 3]
I saw many solutions how we can do this in Pythonic way using list comprehension and so on. But for education purpose I want to now how to add something in Python.
So the question is: what the next step ?
I have downloaded and compiled Python. Can somebody help me with the next step ? To my mind this is quite interesting task.
Many thanks!
3 Answers
Chris Freeman
Treehouse Moderator 68,457 PointsThe short answer is: No. Types defined in C cannot be monkeypatched. Trying to overwrite the list.remove method lead to this error:
In [62]: list.remove = newremove
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
/home/chrisf/devel/pydx-volunteer-2015/pydx_volunteer/<ipython console> in <module>()
TypeError: can't set attributes of built-in/extension type 'list'
This is discussed more on StackOverflow. This SO answer does give a possibility using pypy/forbiddenfruit module.
A better solution would be to create your own list class that has your version of remove:
class MyList(list):
'''Create new List class with altered remove method'''
def remove(self, item):
'''Remove all instances of item from list'''
# "self" is the list
# create new self using list comprehension omitting item
self[:] = [x for x in self if x != item]
Using it:
In [67]: lst = MyList([3, 4, 5, 6, 3, 4, 1, 8, 9, 3, 7, 1, 3])
In [68]: lst
Out[68]: [3, 4, 5, 6, 3, 4, 1, 8, 9, 3, 7, 1, 3]
In [69]: lst.remove(1)
In [70]: lst
Out[70]: [3, 4, 5, 6, 3, 4, 8, 9, 3, 7, 3]
In [71]: lst.remove(3)
In [72]: lst
Out[72]: [4, 5, 6, 4, 8, 9, 7]
# Changing regular list to MyList:
In [73]: lst2 = [1, 0, 1, 0, 1, 0]
In [74]: lst2 = MyList(lst2)
In [75]: lst2
Out[75]: [1, 0, 1, 0, 1, 0]
In [76]: lst2.remove(0)
In [77]: lst2
Out[77]: [1, 1, 1]
Ned Grossy
Courses Plus Student 3,292 PointsYeah, definitely, it is best way to start. Many thanks!
Ned Grossy
Courses Plus Student 3,292 PointsSo,
seems like I did it.
a = [1, 2, 3, 1] a.remove(1, all = True) a # [2, 3]
Looks more attractive than
a = [1, 2, 3, 1] a[:] = (item for item in a if item != 1)
Or especially than another non-Pythonic solutions.
Is it?
Ned Grossy
Courses Plus Student 3,292 PointsNed Grossy
Courses Plus Student 3,292 PointsI mean how to start edit CPython’s source code. I want to add this feature into Python core.
Chris Freeman
Treehouse Moderator 68,457 PointsChris Freeman
Treehouse Moderator 68,457 PointsAh, that's a different beast entirely. There is the Python Developers Guide which details how to work on the core code development.