CODEWITHSUNDEEP
pythonmacospython-2.7
dudu
dudu

Reputation: 849

python 2.x print statement: one print statement results in more than one line

import numpy as np

f=open("a.txt","wb")
a=np.zeros((10,36))
for i in range(10):
  for j in range(36):
    a[i][j]=i+j
for b in a:
  print >>f, b

At first, I think it will occupy 10 lines in the a.txt file with each row in array a a line. But the truth is, the file looks like this: a.txt

It can be seen that each row in a occupies three lines in the file. Why?

Upvotes: 0

Views: 219

Answers (6)

salman
salman

Reputation: 21

When you're iterating your matrix in the second loop, variable b is still a numpy object. When you try to print this numpy object, python first gets its string representation.

Numpy has built-in formatting for pretty-printing this numpy object, which is the reason for the multiple lines.

Upvotes: 2

joris255
joris255

Reputation: 155

Numpy formats the data when it outputs it. However, SciPy doc shows you how you can pimp the output, using for example array2string:

import numpy as np

a = np.zeros((10, 36))

for i, line in enumerate(a):
  for j, column in enumerate(line):
    a[i][j] = i + j

with open("a.txt","wb") as f:
    f.write(np.array2string(a, max_line_width=1000))

Here, with a max_line_width of 1000, each line of the file can be 1000 chars wide.

The file:

[[  0.   1.   2.   3.   4.   5.   6.   7.   8.   9.  10.  11.  12.  13.  14.  15.  16.  17.  18.  19.  20.  21.  22.  23.  24.  25.  26.  27.  28.  29.  30.  31.  32.  33.  34.  35.]
 [  1.   2.   3.   4.   5.   6.   7.   8.   9.  10.  11.  12.  13.  14.  15.  16.  17.  18.  19.  20.  21.  22.  23.  24.  25.  26.  27.  28.  29.  30.  31.  32.  33.  34.  35.  36.]
 [  2.   3.   4.   5.   6.   7.   8.   9.  10.  11.  12.  13.  14.  15.  16.  17.  18.  19.  20.  21.  22.  23.  24.  25.  26.  27.  28.  29.  30.  31.  32.  33.  34.  35.  36.  37.]
 [  3.   4.   5.   6.   7.   8.   9.  10.  11.  12.  13.  14.  15.  16.  17.  18.  19.  20.  21.  22.  23.  24.  25.  26.  27.  28.  29.  30.  31.  32.  33.  34.  35.  36.  37.  38.]
 [  4.   5.   6.   7.   8.   9.  10.  11.  12.  13.  14.  15.  16.  17.  18.  19.  20.  21.  22.  23.  24.  25.  26.  27.  28.  29.  30.  31.  32.  33.  34.  35.  36.  37.  38.  39.]
 [  5.   6.   7.   8.   9.  10.  11.  12.  13.  14.  15.  16.  17.  18.  19.  20.  21.  22.  23.  24.  25.  26.  27.  28.  29.  30.  31.  32.  33.  34.  35.  36.  37.  38.  39.  40.]
 [  6.   7.   8.   9.  10.  11.  12.  13.  14.  15.  16.  17.  18.  19.  20.  21.  22.  23.  24.  25.  26.  27.  28.  29.  30.  31.  32.  33.  34.  35.  36.  37.  38.  39.  40.  41.]
 [  7.   8.   9.  10.  11.  12.  13.  14.  15.  16.  17.  18.  19.  20.  21.  22.  23.  24.  25.  26.  27.  28.  29.  30.  31.  32.  33.  34.  35.  36.  37.  38.  39.  40.  41.  42.]
 [  8.   9.  10.  11.  12.  13.  14.  15.  16.  17.  18.  19.  20.  21.  22.  23.  24.  25.  26.  27.  28.  29.  30.  31.  32.  33.  34.  35.  36.  37.  38.  39.  40.  41.  42.  43.]
 [  9.  10.  11.  12.  13.  14.  15.  16.  17.  18.  19.  20.  21.  22.  23.  24.  25.  26.  27.  28.  29.  30.  31.  32.  33.  34.  35.  36.  37.  38.  39.  40.  41.  42.  43.  44.]]

Upvotes: 1

Dimitris Fasarakis Hilliard
Dimitris Fasarakis Hilliard

Reputation: 160417

You can see by the documentation that the default value for max_line_width is 75. After that numpy issues a \n character. Since you're printing an ndarray with b this is what is used.

To change this you can either set the set_printoptions globally, as already suggested, or if you only want this effect limited to writing in the file you can change your loop to printing by using np.array_str:

for b in a:
  # tweak the line width to what suits you:
  print >>f, np.array_str(c, max_line_width=300)

Upvotes: 0

Robert K.
Robert K.

Reputation: 76

Maybe it woule be better use the numpy function savetxt. Something like this: 

import numpy as np
a = np.zeros((10,36))

for i in range(10):
    for j in range(36):
        a[i][j] = i + j

np.savetxt("a.txt",a,'%2d',newline="\r\n")

So it does the newline only after row of the array :)

Edit:
http://docs.scipy.org/doc/numpy/reference/generated/numpy.savetxt.html

Upvotes: 0

Anton Zuenko
Anton Zuenko

Reputation: 761

The thing is that when you're iterating your matrix in the second loop, b is still numpy object. When you try to print some object, python first gets its string representation. Numpy has built-in formatting for pretty-printing objects, which is actually called. You can fix it by converting to list in the last line: print >>f, list(b)

Upvotes: 0

Dennis Sakva
Dennis Sakva

Reputation: 1467

Numpy limits line length to 75 by default. You can change the default by np.set_printoptions(linewidth=1000)

Upvotes: 2

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