Easy pretty printing of floats in python

Question

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    gt  gt  gt  import print options  gt  gt  gt  print options set float precision 2   gt  gt  gt  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

User · Answer

a    9 0  0 052999999999999999  0 032575399999999997  0 010892799999999999  0 055702500000000002  0 079330300000000006  print  quot    quot  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

User · Answer

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

User · Answer

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   lt --    9 00 0 05 0 03 0 01 0 06 0 08 lt --

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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

User · Answer

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

User · Answer

You can do   a    9 0  0 052999999999999999  0 032575399999999997  0 010892799999999999  0 055702500000000002  0 079330300000000006  print    0 2f    i for i in a

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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

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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

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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    gt  gt  gt  c e alpha eps0    299792458   2 718281828  0 00729735  8 8541878e-12   gt  gt  gt  print prettylist2f c e alpha eps0      299792458 00  2 72  0 01  0 00   gt  gt  gt  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

User · Answer

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

User · Answer

The code below works nice to me   list   map  lambda x  float   0 2f    x   list

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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

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A more permanent solution is to subclass float    gt  gt  gt  class prettyfloat float       def   repr   self           return   0 2f    self   gt  gt  gt  x  1 290192  3 0002  22 119199999999999  3 4110999999999998   gt  gt  gt  x   map prettyfloat  x   gt  gt  gt  x  1 29  3 00  22 12  3 41   gt  gt  gt  y   x 2   gt  gt  gt  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

User · Answer

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

User · Answer

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

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List comps are your friend   print      join    2f    f for f in list o numbers    Try it    gt  gt  gt  nums    9 0  0 052999999999999999  0 032575399999999997  0 010892799999999999   gt  gt  gt  print      join    2f    f for f in nums  9 00  0 05  0 03  0 01

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Note that you can also multiply a string like    2f   example     2f   10     gt  gt  gt  print    2f   len yourlist    tuple yourlist  2 00 33 00 4 42 0 31

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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    gt  gt  gt  ugly    9 0  0 052999999999999999  0 032575399999999997              0 010892799999999999  0 055702500000000002  0 079330300000000006   gt  gt  gt  prettylist   lambda l      s          join    2f    f for f in l   gt  gt  gt  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

User · Answer

As noone 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

[python] Easy pretty printing of floats in python?

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