data truncate when str(time.time()) in Python

Question

Can anyone tell me what happened when str(time.time()) runs? It seems the data has been truncated, but it recovered when float(str(time.time())) runs. I'm so confused.

In [1]: import time

In [2]: a = time.time()

In [3]: a
Out[3]: 1445007755.321532

In [4]: str(a)
Out[4]: '1445007755.32'

In [6]: a.__str__()
Out[6]: '1445007755.32'

In [7]: float(a)
Out[7]: 1445007755.321532

Answer 1

Calling str(a) does not modify a, so there is no reason why float(a) should depend on str(a). Maybe you wanted to reassign a?

a = 1445007755.321532
a = str(a)
float(a)

In this case the result is different:

>>> a = 1445007755.321532
>>> b = str(a)
>>> a == float(b)
False
>>> a, b, float(b)
(1445007755.321532, '1445007755.32', 1445007755.32)

---

Note that it holds that float(x) == x if x is already a float, so what you see is not surprising at all.

^{Even more: float(x) is x if x is of type float.}

If you wonder why str seems to truncate the number it is because it returns a "human readable" representation of the value as a string.

If you want an "exact" representation use repr, or simply use a proper formatting function like: "%.6f" % a to control the number of decimal digits etc.