👻 Check our latest review to choose the best laptop for Machine Learning engineers and Deep learning tasks!
This was my source I started with.
My List
L = [0, 23, 234, 89, None, 0, 35, 9]
When I run this :
L = filter(None, L)
I get this results
[23, 234, 89, 35, 9]
But this is not what I need, what I really need is :
[0, 23, 234, 89, 0, 35, 9]
Because I"m calculating percentile of the data and the 0 make a lot of difference.
How to remove the None value from a list without removing 0 value?
👻 Read also: what is the best laptop for engineering students?
List comprehension vs. lambda + filter
5 answers
I happened to find myself having a basic filtering need: I have a list and I have to filter it by an attribute of the items.
My code looked like this:
my_list = [x for x in my_list if x.attribute == value]
But then I thought, wouldn"t it be better to write it like this?
my_list = filter(lambda x: x.attribute == value, my_list)
It"s more readable, and if needed for performance the lambda could be taken out to gain something.
Question is: are there any caveats in using the second way? Any performance difference? Am I missing the Pythonic Way‚Ñ¢ entirely and should do it in yet another way (such as using itemgetter instead of the lambda)?
Answer #1
It is strange how much beauty varies for different people. I find the list comprehension much clearer than filter+lambda, but use whichever you find easier.
There are two things that may slow down your use of filter.
The first is the function call overhead: as soon as you use a Python function (whether created by def or lambda) it is likely that filter will be slower than the list comprehension. It almost certainly is not enough to matter, and you shouldn"t think much about performance until you"ve timed your code and found it to be a bottleneck, but the difference will be there.
The other overhead that might apply is that the lambda is being forced to access a scoped variable (value). That is slower than accessing a local variable and in Python 2.x the list comprehension only accesses local variables. If you are using Python 3.x the list comprehension runs in a separate function so it will also be accessing value through a closure and this difference won"t apply.
The other option to consider is to use a generator instead of a list comprehension:
def filterbyvalue(seq, value):
for el in seq:
if el.attribute==value: yield el
Then in your main code (which is where readability really matters) you"ve replaced both list comprehension and filter with a hopefully meaningful function name.
Answer #2
This is a somewhat religious issue in Python. Even though Guido considered removing map, filter and reduce from Python 3, there was enough of a backlash that in the end only reduce was moved from built-ins to functools.reduce.
Personally I find list comprehensions easier to read. It is more explicit what is happening from the expression [i for i in list if i.attribute == value] as all the behaviour is on the surface not inside the filter function.
I would not worry too much about the performance difference between the two approaches as it is marginal. I would really only optimise this if it proved to be the bottleneck in your application which is unlikely.
Also since the BDFL wanted filter gone from the language then surely that automatically makes list comprehensions more Pythonic ;-)
How do I do a not equal in Django queryset filtering?
5 answers
In Django model QuerySets, I see that there is a __gt and __lt for comparative values, but is there a __ne or != (not equals)? I want to filter out using a not equals. For example, for
Model:
bool a;
int x;
I want to do
results = Model.objects.exclude(a=True, x!=5)
The != is not correct syntax. I also tried __ne.
I ended up using:
results = Model.objects.exclude(a=True, x__lt=5).exclude(a=True, x__gt=5)
Answer #1
You can use Q objects for this. They can be negated with the ~ operator and combined much like normal Python expressions:
from myapp.models import Entry
from django.db.models import Q
Entry.objects.filter(~Q(id=3))
will return all entries except the one(s) with 3 as their ID:
[<Entry: Entry object>, <Entry: Entry object>, <Entry: Entry object>, ...]
We hope this article has helped you to resolve the problem. Apart from remove None value from a list without removing the 0 value, check other code Python module-related topics.
Want to excel in Python? See our review of the best Python online courses 2023. If you are interested in Data Science, check also how to learn programming in R.
By the way, this material is also available in other languages:
- Italiano remove None value from a list without removing the 0 value
- Deutsch remove None value from a list without removing the 0 value
- Français remove None value from a list without removing the 0 value
- Español remove None value from a list without removing the 0 value
- Türk remove None value from a list without removing the 0 value
- Русский remove None value from a list without removing the 0 value
- Português remove None value from a list without removing the 0 value
- Polski remove None value from a list without removing the 0 value
- Nederlandse remove None value from a list without removing the 0 value
- 中文 remove None value from a list without removing the 0 value
- 한국어 remove None value from a list without removing the 0 value
- 日本語 remove None value from a list without removing the 0 value
- हिन्दी remove None value from a list without removing the 0 value
Tallinn | 2023-01-27
Maybe there are another answers? What remove None value from a list without removing the 0 value exactly means?. I just hope that will not emerge anymore
Shanghai | 2023-01-27
I was preparing for my coding interview, thanks for clarifying this - remove None value from a list without removing the 0 value in Python is not the simplest one. I am just not quite sure it is the best method
Texas | 2023-01-27
Maybe there are another answers? What remove None value from a list without removing the 0 value exactly means?. I just hope that will not emerge anymore
