Argthtjtr

I am trying to generate (something like) the following dictionary:

funcs1 = {

    '0':lambda x:x==0,

    '1':lambda x:x==1,

    '2':lambda x:x==2,

    '3':lambda x:x==3,

    '4':lambda x:x==4,

    '5':lambda x:x==5,

}

I tried to create the dictionary with a list comprehension like this:

funcs2 = {str(i):lambda x:x==i for i in range(0,6)}

Or simply using a for loop:

funcs3 = {}

for i in range(0,6):

    funcs3.update({str(i): lambda x:x==i})

However, funcs2 and funcs3 are not the same as funcs1, for example, when calling the element '0' of each one of them and applying it to 0, the results are different:

funcs1['0'](0)

Out[2]: True



funcs2['0'](0)

Out[3]: False



funcs3['0'](0)

Out[4]: False

Can somebody please help me out and point out where I am making a mistake?

This is a common misunderstanding caused by Python late binding, this should fix your code:

funcs1 = {

    '0': lambda x: x == 0,

    '1': lambda x: x == 1,

    '2': lambda x: x == 2,

    '3': lambda x: x == 3,

    '4': lambda x: x == 4,

    '5': lambda x: x == 5,

}



funcs2 = {str(i): lambda x, i=i: x == i for i in range(0, 6)}



funcs3 = {}

for i in range(0, 6):

    funcs3.update({str(i): lambda x, i=i: x == i})



print(funcs1['0'](0))

print(funcs2['0'](0))

print(funcs3['0'](0))

Output

True

True

True

This works:

>>> def make_fn(i):

...     def fn(x):

...         return x==i

...     return fn

...

>>> funcs = {str(i): make_fn(i) for i in range(6)}

Testing, I get:

>>> funcs['0'](0)

True

>>> funcs['1'](1)

True

>>> funcs['0'](1)

False