On 29/08/2020 08:58, Shivlal Sharma wrote:
from functools import*
nums = [1, 2, 3, 4, 5, 6, 7, 8, 9]
add = reduce(lambda a : a + 1, nums)
print(add)
error: -
TypeError Traceback (most recent call last)
<ipython-input-15-684b5d4fac30> in <module>()
1 from functools import*
2 nums = [1, 2, 3, 4, 5, 6, 7, 8, 9]
----> 3 add = reduce(lambda a : a + 1, nums)
4 print(add)
TypeError: <lambda>() takes 1 positional argument but 2 were given
When you write
lambda a :
you are defining a function that takes **one** argument, viz. a.
It's the same as if you wrote:
def myfunc(a): return a+1
and then
add = reduce(myfunc, nums)
But reduce always calls your supplied function with **two** arguments.
Hence the error.
I don't know exactly what you are trying to do, but if you wrote
add = reduce(lambda a,b: a+1, nums)
or equivalently
def myfunc(a,b): return a+1
add = reduce(myfunc, nums)
reduce would call your lambda function succesively with arguments
(1,2) # which would return 1+1 i.e. 2
(2,3) # use previous result (2) and next number in the sequence
(3); returns 2+1 i.e. 3
(3,4) # use previous result (3) and next number in the sequence (4)
.....
(8,9) # returns 8+! i.e. 9
and finally 9 would be printed.
If you want to watch what is happening try
def myfunc(a,b):
print(f"Myfunc({a},{b})")
return a+1
add = reduce(myfunc, nums)
Try
from functools import *
help(reduce)
for an explanation of how reduce works. Note that the first sentence
starts "Apply a function of two arguments"
Best wishes
Rob Cliffe
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