# Pretty printing of the numpy ndarrays

Following this idea for pretty printing of numpy ndarrays, I have developed a very primitive prototype:

def ndtotext(A, w=None, h=None):
if A.ndim==1:
if w == None :
return str(A)
else:
s ='['+' '*(max(w[-1],len(str(A[0])))-len(str(A[0]))) +str(A[0])
for i,AA in enumerate(A[1:]):
s += ' '*(max(w[i],len(str(AA)))-len(str(AA))+1)+str(AA)
s +='] '
elif A.ndim==2:
w1 = [max([len(str(s)) for s in A[:,i]])  for i in range(A.shape[1])]
w0 = sum(w1)+len(w1)+1
s= u'\u250c'+u'\u2500'*w0+u'\u2510' +'\n'
for AA in A:
s += ' ' + ndtotext(AA, w=w1) +'\n'
s += u'\u2514'+u'\u2500'*w0+u'\u2518'
elif A.ndim==3:
h=A.shape[1]
s1=u'\u250c' +'\n' + (u'\u2502'+'\n')*h + u'\u2514'+'\n'
s2=u'\u2510' +'\n' + (u'\u2502'+'\n')*h + u'\u2518'+'\n'
strings=[ndtotext(a)+'\n' for a in A]
strings.append(s2)
strings.insert(0,s1)
s='\n'.join(''.join(pair) for pair in zip(*map(str.splitlines, strings)))
return s


for example:

shape = 4, 5, 3
C=np.random.randint(10000, size=np.prod(shape)).reshape(shape)
print(ndtotext(C))

┌┌────────────────┐┌────────────────┐┌────────────────┐┌────────────────┐┐
│ [9298 4404 1759]  [5426 3488 9267]  [8884 7721  579]  [6872 4226 1858] │
│ [6723  271 8466]  [9885 6760 8949]  [ 295 7422 5659]  [5322 4239 7446] │
│ [7156 6077 9390]  [2712 6379 2832]  [6956  626 5534]  [ 142 4090 6390] │
│ [9377 9033 1953]  [8986 3791 4538]  [2466 8572  662]  [1528 8922 9656] │
│ [1449 7319 3939]  [7350 9619  928]  [7542 4704 1477]  [ 980 6037  869] │
└└────────────────┘└────────────────┘└────────────────┘└────────────────┘┘


I would appreciate if you could review this code and let me know how I can improve it.

What I hope to see:

• possible mistakes or cases to break the code
• how to make it faster, more performant, pythonic
• how to extend it to higher dimensions

P.S. For those who follow up this idea I have integrated everythin here in this Jupyter Notebook

• How many dimensions does this work with? 1-3. – Peilonrayz Nov 7 '18 at 13:26
• @Peilonrayz this one works 1-3 but the HTML version developed by others might work for further dimensions too. I haven't checked. It would be great if we could extend this to all dimensions. I guess doing some text/string work plus recursion this should be doable. – Foad Nov 7 '18 at 13:29
• Can you modify your example to actually include how to call your function? I.e. what should w look like? – Graipher Nov 7 '18 at 13:56
• @Foad: Well, it is mostly trivial, but for the 1D case it is not so clear to me what and if anything should be passed for w. – Graipher Nov 7 '18 at 14:02
• @Graipher my apologies. yeah the w thing is very badly implemented. I'm actually very embarrassed by it. please help me know how if you can think of a better approach. – Foad Nov 7 '18 at 14:05

## 1 Answer

If A.ndim is not in 1, 2, 3, your code tries to return a non-existing string s. It would be better to be explicit about what your code supports atm:

def ndtotext(A, w=None, h=None):
...
else:
raise NotImplementedError("Currently only 1 - 3 dimensions are supported")
return s


While we are at the point of having your code be clear about what is happening, you should add a docstring explaining what your code does:

def ndtotext(A, w=None, h=None):
"""Returns a string to pretty print the numpy.ndarray A.

Currently supports 1 - 3 dimensions only.
Raises a NotImplementedError if an array with more dimensions is passed.

Describe w and h.
"""
...


Next, Python has an official style-guide, PEP8, which programmers are encouraged to follow. One of the things it recommends is surrounding operators with spaces (which I fixed in the rest of the code) and using lower_case for variables and functions (which I left as is for now).

Now, let's come to your actual code:

• You calculate some values multiple times (like str(A[0])), save those to a variable.
• If you want to compare to None, use is (since it is a singleton).
• No else needed after an if...return (this is a matter of personal style, I prefer not having the additional level of indentation).
• Use str.rjust to add enough whitespace in front of your strings. You could also use str.format for this, but it looks less nice.
• Your w has a weird structure, with the width of the first column being the last entry and the rest starting at zero.
• Give the unicode values names. And then add functions to draw a line of specified length.
• String addition is costly and slow. Try to consistently use building a list and str.joining it.

UPPER_LEFT = u'\u250c'
UPPER_RIGHT = u'\u2510'
LOWER_LEFT = u'\u2514'
LOWER_RIGHT = u'\u2518'
HORIZONTAL = u'\u2500'
VERTICAL = u'\u2502'

def upper_line(width):
return UPPER_LEFT + HORIZONTAL * width + UPPER_RIGHT

def lower_line(width):
return LOWER_LEFT + HORIZONTAL * width + LOWER_RIGHT

def left_line(height):
return "\n".join([UPPER_LEFT] + [VERTICAL] * height + [LOWER_LEFT])

def right_line(height):
return "\n".join([UPPER_RIGHT] + [VERTICAL] * height + [LOWER_RIGHT])

def ndtotext(A, w=None, h=None):
"""Returns a string to pretty print the numpy.ndarray A.

Currently supports 1 - 3 dimensions only.
Raises a NotImplementedError if an array with more dimensions is passed.

Describe w and h.
"""
if A.ndim == 1:
if w is None:
return str(A)
s = " ".join([str(value).rjust(width) for value, width in zip(A, w)])
return '[{}]'.format(s)
elif A.ndim == 2:
widths = [max([len(str(s)) for s in A[:, i]]) for i in range(A.shape[1])]
s = "".join([' ' + ndtotext(AA, w=widths) + ' \n' for AA in A])
w0 = sum(widths) + len(widths) - 1 + 2 # spaces between elements and corners
return upper_line(w0) + '\n'  + s + lower_line(w0)
elif A.ndim == 3:
h = A.shape[1]
strings = [left_line(h)]
strings.extend(ndtotext(a) + '\n' for a in A)
strings.append(right_line(h))
return '\n'.join(''.join(pair) for pair in zip(*map(str.splitlines, strings)))
raise NotImplementedError("Currently only 1 - 3 dimensions are supported")


This can probably be even more compactified, but I think it is a good start.

Example usage:

x = np.arange(12)

print(ndtotext(x))
[ 0  1  2  3  4  5  6  7  8  9 10 11]

print(ndtotext(x.reshape(3, 4)))
┌───────────┐
[0 1  2  3]
[4 5  6  7]
[8 9 10 11]
└───────────┘

print(ndtotext(x.reshape(3, 2, 2)))
┌┌─────┐┌─────┐┌───────┐┐
│ [0 1]  [4 5]  [ 8  9] │
│ [2 3]  [6 7]  [10 11] │
└└─────┘└─────┘└───────┘┘

• wow. awesome. thanks a lot. I'm gonna try your points and get back here. – Foad Nov 7 '18 at 15:36
• You code does not work properly. I edited it so it works but for some reason my edit was rejected! – Foad Nov 10 '18 at 18:19
• @Foad: You are right, fixed it and added examples. – Graipher Nov 11 '18 at 13:02
• I'm integrating all the results, including your suggestions here in this Notebook. – Foad Nov 12 '18 at 10:41