python - Why is my range function printing untruncated floats? -


i made range function have other integer step, , works, wondering why floats not truncated.

def drange(start, step): values = [] r = start while r >= 0: values.append(r) r += step return values print drange(2, -0.2)

upon debugging find instead of printing

[2, 1.8, 1.6, 1.4, 1.2, 1.0, 0.8, 0.6, 0.4, 0.2, 0]

it instead prints

[2, 1.8, 1.6, 1.4000000000000001, 1.2000000000000002, 1.0000000000000002, 0.8000 000000000003, 0.6000000000000003, 0.4000000000000003, 0.2000000000000003, 2.7755 575615628914e-16]

lol, no wonder module isn't working. why happen , how might fix it?

this correct behavior, since 1 cannot express 0.2 = 1/5 in base 2, there no way express 1/3 in base 10.

use decimal instead if want calculate in base 10.

additionally, should use generator, in

def drange(start, step): r = start while r >= 0: yield r r += step print list(drange(2, -0.2))

that allows users of drange iterate on values without memory being allocated whole list.


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