让 Python 找到两个满足条件的整数

Question

Set-up

I'm looking for all the integer pairs (x,y) in 2 closed sets: [822,2000] and [506,1231] such that x/y=1.624 .

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Code so far

I tried,

a = [[(x,y)] for x in range(822,2001) and y in range(506,1232) if x/y = 1.624]

But this gives a SyntaxError: invalid syntax pointing to the = in the code.

And if I do,

a = [[(x,y)] for x in range(822,2001) and y in range(506,1232) if x/y <= 1.624]

I get NameError: name 'y' is not defined .

How do I solve this?

Answer 1

Comparing float calculations with == is difficult due to the nature of float arithmetics.

It is often better to compare like this:

a = [(x,y) for x in range(822,2001) for y in range(506,1232) if abs(x/y - 1.624) < 0.00001] 
print(set(a)) 

By substracting the wanted value from your result and and comparing its absolute value against something kindof small you get better results.

Result (using a set):

{(1624, 1000), (1637, 1008), (1015, 625), (1611, 992), (1840, 1133), 
 (1814, 1117), (1827, 1125), (1408, 867), (1218, 750), (1434, 883), 
 (1421, 875)}

Python rounding error with float numbers

Answer 2

For the first one you are using the assignment operator instead of the equivalent operator so it should be:

a = [[(x,y)] for x in range(822,2001) and y in range(506,1232) if x/y == 1.624]

And for the second you're probably better off using two for loops

a = [[(x,y)] for x in range(822,2001) for y in range(506,1232) if x/y <= 1.624]

The second one would not make sense as you said it because x and y are coming from lists that have an unequal number of elements so you cannot loop over them like that