appending to list in list comprehension

Question

I am trying to get the minimum of a list and float, I had the following code but it was giving error

x=['14.99', '14.99', '15.00', '16.36']
y=21.00
min([float(i) for i in x.append(y)])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not iterable
#x= ['14.99', '14.99', '15.00', '16.36', 21.0] y got appended

However, if i do (append y before list comprehension)

x=['14.99', '14.99', '15.00', '16.36']
y=21.00
x.append(y)
min([float(i) for i in x])

Output is :14.99 #correct

How can I do this in one line?

``list.append()`` always returns ``None``, if that's what you're asking, same with most other list manipulation methods. — Mike Scotty, Jun 24 '19 at 13:16
Yes, but that's not the point. You are trying to iterate the **return value** of ``x.append(y)``, which is ``None``. — Mike Scotty, Jun 24 '19 at 13:19

score 3 · Accepted Answer · answered Jun 24 '19 at 13:28

3

try this

min(y, min([float(i) for i in x]))

or this one is more readable

min(y, min(map(float, x)))

basically you compare the float y with the minimum of the list.

answered Jun 24 '19 at 13:28

Emmet B

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I want the minimum of the 5 items not the minimum of the list – programmerwiz32 Jun 24 '19 at 13:32
@programmerwiz32 those will give the minimum of the 5 items. You can check by setting y=11 for example, it will give 11. – Emmet B Jun 24 '19 at 13:34

score 1 · Answer 2 · answered Jun 24 '19 at 13:22

1

It's very ugly in my opinion, but you can do it like that:

min([float(i) for i in x+[y])])

answered Jun 24 '19 at 13:22

alec_djinn

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what is a better looking way – programmerwiz32 Jun 24 '19 at 13:23
1

The "better looking way" is IMHO to keep your original code. It's more readable and should even be more efficient (appending to an existing object instead of creating a new one - or rather two new ones, since you're creating a new list from ``y`` first and then another new list from ``x`` and ``[y]``). – Mike Scotty Jun 24 '19 at 13:25
I would use 2 lines to be explicit: `_list = [float(i) for i in x]+[y]` and then `min(_list)`. If you do not care overwriting x, then the code you posted is the best one. – alec_djinn Jun 24 '19 at 13:26

score 0 · Answer 3 · answered Jun 24 '19 at 13:26

0

x=['14.99', '14.99', '15.00', '16.36']
y=21.00
min(float(x) for x in x+[y])

This concatenates y as a list to the x list, and then finds the min of all of them.

See Allow python list append method to return the new list.

answered Jun 24 '19 at 13:26

blackbrandt

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appending to list in list comprehension

3 Answers3