python: converting numpy array to fixed float numbers

Question

I am dealing with a Python function that compute geometrical center for all elements of nestled array representing XYZ coordinates

 def lig_center(nested_array_list):
 a = numpy.array(nested_array_list)
 mean = numpy.mean(a, axis=0)
 return mean[0], mean[1], mean[2] # x, y, z
 
# input list 
xyz= [[121.133, 146.696, 139.126], [121.207, 145.489, 138.437], [122.058, 145.337, 137.335], [121.972, 143.689, 136.593], [123.209, 143.616, 135.31], [124.536, 143.881, 135.697], [124.87, 145.234, 135.928], [126.179, 145.569, 136.301], [127.156, 144.591, 136.455], [126.838, 143.258, 136.229], [123.824, 146.34, 135.736], [125.543, 142.913, 135.853], [123.008, 142.449, 134.454], [120.662, 143.598, 135.938], [122.362, 142.722, 137.625], [122.857, 146.427, 136.913], [122.764, 147.633, 137.625], [121.914, 147.77, 138.718], [123.101, 146.373, 134.374], [122.534, 147.208, 134.333], [122.482, 145.576, 134.33], [124.016, 146.346, 133.138], [125.066, 147.46, 133.272], [124.449, 148.847, 133.177], [123.972, 149.313, 131.947], [123.409, 150.582, 131.856], [123.322, 151.385, 132.993], [123.796, 150.925, 134.221], [124.36, 149.655, 134.314], [122.769, 152.634, 132.905], [123.339, 153.323, 133.255]]
# calculate geonetrical center of each element of xyz
col=lig_center(xyz)
# result"(123.51000000000001, 146.66999999999999, 135.30000000000001)

how I could obtain result of col in the following format:

# just three float numbers with fixed number of digits after .
123.510 146.669 135.300

• Tarik: 1. Read "what every programmer should know about floating point numbers". 2. Handle this by formatting the numbers upon output, specifying 3 digits and you will get the effect you want.
• user14748664: I could print it directly from function #print("[%.3f, %.3f, %.3f]" % tuple(mean)) BUT I need to save this in a variable returned to the script

Answer 1

Use numpy.around to round all values in an array to a specified number of decimals:

import numpy as np
...
col = np.around(col, 3)

• user14748664: I have already tried it. It gives sometimes less number of digits in some values: for example array([ 123.51, 146.67, 135.3 ]), while I need to keep the same number in all three numbers
• dschurman: The smaller number of digits means that the float was fully rounded, i.e. only 0's after the point it stops. If you truly need consistent formatting like this, you'll have to convert to strings, for example list(map(lambda x: format(x, ".3f"), col))