Easy pretty printing of floats?
PythonPrintingFormattingFloating PointPython Problem Overview
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]
Python Solutions
Solution 1 - Python
As no one has added it, it should be noted that going forward from Python 2.6+ the recommended way to do string formating is with format
, to get ready for Python 3+.
print ["{0:0.2f}".format(i) for i in a]
The new string formating syntax is not hard to use, and yet is quite powerfull.
I though that may be pprint
could have something, but I haven't found anything.
Solution 2 - Python
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]
Solution 3 - Python
You can do:
a = [9.0, 0.052999999999999999, 0.032575399999999997, 0.010892799999999999, 0.055702500000000002, 0.079330300000000006]
print ["%0.2f" % i for i in a]
Solution 4 - Python
It's an old question but I'd add something potentially useful:
I know you wrote your example in raw Python lists, but if you decide to use numpy
arrays instead (which would be perfectly legit in your example, because you seem to be dealing with arrays of numbers), there is (almost exactly) this command you said you made up:
import numpy as np
np.set_printoptions(precision=2)
Or even better in your case if you still want to see all decimals of really precise numbers, but get rid of trailing zeros for example, use the formatting string %g
:
np.set_printoptions(formatter={"float_kind": lambda x: "%g" % x})
For just printing once and not changing global behavior, use np.array2string
with the same arguments as above.
Solution 5 - Python
Note that you can also multiply a string like "%.2f" (example: "%.2f "*10).
>>> print "%.2f "*len(yourlist) % tuple(yourlist)
2.00 33.00 4.42 0.31
Solution 6 - Python
The most easy option should be to use a rounding routine:
import numpy as np
x=[9.0, 0.052999999999999999, 0.032575399999999997, 0.010892799999999999, 0.055702500000000002, 0.079330300000000006]
print('standard:')
print(x)
print("\nhuman readable:")
print(np.around(x,decimals=2))
This produces the output:
standard:
[9.0, 0.053, 0.0325754, 0.0108928, 0.0557025, 0.0793303]
human readable:
[ 9. 0.05 0.03 0.01 0.06 0.08]
Solution 7 - Python
print "[%s]"%", ".join(map(str,yourlist))
This will avoid the rounding errors in the binary representation when printed, without introducing a fixed precision constraint (like formating with "%.2f"
):
[9.0, 0.053, 0.0325754, 0.0108928, 0.0557025, 0.0793303]
Solution 8 - Python
l = [9.0, 0.052999999999999999, 0.032575399999999997, 0.010892799999999999, 0.055702500000000002, 0.079330300000000006]
Python 2:
print ', '.join('{:0.2f}'.format(i) for i in l)
Python 3:
print(', '.join('{:0.2f}'.format(i) for i in l))
Output:
9.00, 0.05, 0.03, 0.01, 0.06, 0.08
Solution 9 - Python
To control the number of significant digits, use the format specifier %g.
Let's name Emile's solution prettylist2f. Here is the modified one:
prettylist2g = lambda l : '[%s]' % ', '.join("%.2g" % x for x in l)
Usage:
>>> c_e_alpha_eps0 = [299792458., 2.718281828, 0.00729735, 8.8541878e-12]
>>> print(prettylist2f(c_e_alpha_eps0)) # [299792458.00, 2.72, 0.01, 0.00]
>>> print(prettylist2g(c_e_alpha_eps0)) # [3e+08, 2.7, 0.0073, 8.9e-12]
If you want flexibility in the number of significant digits, use f-string formatting instead:
prettyflexlist = lambda p, l : '[%s]' % ', '.join(f"{x:.{p}}" for x in l)
print(prettyflexlist(3,c_e_alpha_eps0)) # [3e+08, 2.72, 0.0073, 8.85e-12]
Solution 10 - Python
List comps are your friend.
print ", ".join("%.2f" % f for f in list_o_numbers)
Try it:
>>> nums = [9.0, 0.052999999999999999, 0.032575399999999997, 0.010892799999999999]
>>> print ", ".join("%.2f" % f for f in nums)
9.00, 0.05, 0.03, 0.01
Solution 11 - Python
I believe that Python 3.1 will print them nicer by default, without any code changing. But that is useless if you use any extensions that haven't been updated to work with Python 3.1
Solution 12 - Python
As of Python 3.6, you can use f-strings:
list_ = [9.0, 0.052999999999999999,
0.032575399999999997, 0.010892799999999999,
0.055702500000000002, 0.079330300000000006]
print(*[f"{element:.2f}" for element in list_])
#9.00 0.05 0.03 0.01 0.06 0.08
You can use print parameters while keeping code very readable:
print(*[f"{element:.2f}" for element in list_], sep='|', end='<--')
#9.00|0.05|0.03|0.01|0.06|0.08<--
Solution 13 - Python
You could use pandas.
Here is an example with a list:
In: import pandas as P
In: P.set_option('display.precision',3)
In: L = [3.4534534, 2.1232131, 6.231212, 6.3423423, 9.342342423]
In: P.Series(data=L)
Out:
0 3.45
1 2.12
2 6.23
3 6.34
4 9.34
dtype: float64
If you have a dict d, and you want its keys as rows:
In: d
Out: {1: 0.453523, 2: 2.35423234234, 3: 3.423432432, 4: 4.132312312}
In: P.DataFrame(index=d.keys(), data=d.values())
Out:
0
1 0.45
2 2.35
3 3.42
4 4.13
And another way of giving dict to a DataFrame:
P.DataFrame.from_dict(d, orient='index')
Solution 14 - Python
First, elements inside a collection print their repr. you should learn about __repr__
and __str__
.
This is the difference between print repr(1.1) and print 1.1. Let's join all those strings instead of the representations:
numbers = [9.0, 0.053, 0.0325754, 0.0108928, 0.0557025, 0.07933]
print "repr:", " ".join(repr(n) for n in numbers)
print "str:", " ".join(str(n) for n in numbers)
Solution 15 - Python
I just ran into this problem while trying to use pprint to output a list of tuples of floats. Nested comprehensions might be a bad idea, but here's what I did:
tups = [ (12.0, 9.75, 23.54), (12.5, 2.6, 13.85), (14.77, 3.56, 23.23), (12.0, 5.5, 23.5) ]
pprint([['{0:0.02f}'.format(num) for num in tup] for tup in tups])
I used generator expressions at first, but pprint just repred the generator...
Solution 16 - Python
I had this problem, but none of the solutions here did exactly what I wanted (I want the printed output to be a valid python expression), so how about this:
prettylist = lambda l : '[%s]' % ', '.join("%.2f" % f for f in l)
Usage:
>>> ugly = [9.0, 0.052999999999999999, 0.032575399999999997,
0.010892799999999999, 0.055702500000000002, 0.079330300000000006]
>>> prettylist = lambda l : '[%s]' % ', '.join("%.2f" % f for f in l)
>>> print prettylist(ugly)
[9.00, 0.05, 0.03, 0.01, 0.06, 0.08]
(I know .format() is supposed to be the more standard solution, but I find this more readable)
Solution 17 - Python
a = [9.0, 0.052999999999999999, 0.032575399999999997, 0.010892799999999999, 0.055702500000000002, 0.079330300000000006]
print(", ".join(f'{x:.2f}' for x in a))
f'{x}'
means f-string equal to str(x)
; f'{x:.2f}'
means x
will be present as float number with two decimal places.
Solution 18 - Python
I agree with SilentGhost's comment, the for loop isn't that bad. You can achieve what you want with:
l = [9.0, 0.052999999999999999, 0.032575399999999997, 0.010892799999999999, 0.055702500000000002, 0.079330300000000006]
for x in l: print "%0.2f" % (x)
Solution 19 - Python
The code below works nice to me.
list = map (lambda x: float('%0.2f' % x), list)