static_rtti static_rtti - 24 days ago 9
Python Question

Easy pretty printing of floats in python?

I have a list of floats. If I simply

print
it, it shows up like this:

[9.0, 0.052999999999999999, 0.032575399999999997, 0.010892799999999999, 0.055702500000000002, 0.079330300000000006]


I could use
print "%.2f"
, which would require a
for
loop to traverse the list, but then it wouldn't work for more complex data structures.
I'd like something like (I'm completely making this up)

>>> import print_options
>>> print_options.set_float_precision(2)
>>> print [9.0, 0.052999999999999999, 0.032575399999999997, 0.010892799999999999, 0.055702500000000002, 0.079330300000000006]
[9.0, 0.05, 0.03, 0.01, 0.06, 0.08]

Answer

A more permanent solution is to subclass float:

>>> class prettyfloat(float):
    def __repr__(self):
        return "%0.2f" % self

>>> x
[1.290192, 3.0002, 22.119199999999999, 3.4110999999999998]
>>> x = map(prettyfloat, x)
>>> x
[1.29, 3.00, 22.12, 3.41]
>>> y = x[2]
>>> y
22.12

The problem with subclassing float is that it breaks code that's explicitly looking for a variable's type. But so far as I can tell, that's the only problem with it. And a simple x = map(float, x) undoes the conversion to prettyfloat.

Tragically, you can't just monkey-patch float.__repr__, because float's immutable.

If you don't want to subclass float, but don't mind defining a function, map(f, x) is a lot more concise than [f(n) for n in x]