I have the following code:
g = lambda a, b, c: sum(a, b, c)
print g([4,6,7])
How do I get the lambda function to expand the list into 3 values?
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7 Answers
Expand the list t0 3 values can be done by this:
g(*[4,6,7])
But the sum won't work in your way.
Or you can write this way:
>>> g = lambda *arg: sum(arg)
>>> print g(4, 5, 6)
15
>>>
Or just make your lambda accept a list:
g = lambda alist: sum(alist)
print g([4,6,7])
Comments
Why can't you change lambda to take a list. Because sum() doesn't take three arguments:
>>> g = lambda a_list: sum(a_list)
>>> print g([4,6,7])
17
or a non-keyword argument:
>>> g = lambda *nkwargs: sum(nkwargs)
>>> print g(4,6,7)
17
Comments
g = lambda L: sum(L)
print g([4,6,7])
would work for any arbitrarily sized list.
If you want to use g = lambda a, b, c: someFunc(a, b, c), then call print g(4,6,7)
1 Comment
zhangyangyu
You answer is wrong, the
sum can not accept there arguments.You're defining a function which takes three parameters, and the supplying it with a single parameter, a list. If you want
print g([4,6,7])
to work, your definition should be
g = lambda lst: sum(lst)
Comments
The code you are looking for is:
>>> g = lambda a, b, c: sum([a, b, c])
>>> print g(*[4,6,7])
17
What you were trying to do wont work:
>>> g = lambda a, b, c: sum(a, b, c)
>>> print g(*[4,6,7])
Traceback (most recent call last):
File "<pyshell#83>", line 1, in <module>
print g(*[4,6,7])
File "<pyshell#82>", line 1, in <lambda>
g = lambda a, b, c: sum(a, b, c)
TypeError: sum expected at most 2 arguments, got 3
Because sum() can't handle the arguments you gave it.
Since your lambda function is simply a sum() function, why not just call sum() directly?
If your code the following a, b, c values:
>>> a, b, c = range(1,4)
>>> print a,b,c
1 2 3
And you wanted to do:
>>> g = lambda a, b, c: sum([a, b, c])
>>> print g(*[a,b,c])
6
Why not just do the following?:
>>> sum([a,b,c])
6
1 Comment
smac89
This is an example, I am trying to do something else but the lambda parameters are what I wanted to know about.
>>> g=lambda *l: sum(l)
>>> print g(1,2,3)
6
Comments
If your lambda expects to have a list/tuple of fixed length passed in, but wants to expand the values in that list/tuple into separate parameter variables, the following will work.
g = lambda (a, b, c): a + b + c
g([4, 6, 7])
Note the parentheses around the parameter list.
This "feature" works in Python 2.x, but was removed in Python 3
