Python - How to set the fmt option in numpy.savetxt()?

Learn, how to set the fmt option in numpy.savetxt() in Python?
Submitted by Pranit Sharma, on March 25, 2023

Setting the fmt option in numpy.savetxt()

The numpy.savetxt() is used to save an array to a text file. It accepts many parameters which include x (data to be saved), delimiter (string or character which separated the columns) and fmt.

The fmt is a string type or sequence of string type parameters that represent a sequence of formats or a multi-format string.

For example, in Iteration %d – %10.5f, delimiter is ignored. If the data is complex, there are some legal formats:

  • a single specifier, fmt='%.4e', resulting in numbers formatted like ' (%s+%sj)' % (fmt, fmt)
  • a full string specifying every real and imaginary part, e.g. ' %.4e %+.4ej %.4e %+.4ej %.4e %+.4ej'for 3 columns
  • a list of specifiers, one per column - in this case, the real and imaginary part smust have separate specifiers, e.g. ['%.3e + %.3ej', '(%.15e%+.15ej)']for 2 columns.

In broader context, we can add or modify the data in certain format using the fmt parameter. If we need toset a float precision, we can use fmt='%1.3f'.

Python code to set the fmt option in numpy.savetxt()

# Import numpy
import numpy as np

# Creating a numpy array
arr = np.arange(0.0,5.0,1.0)

# Display original array
print("Original array:\n",arr,"\n")

# Saving data with a specific format
np.savetxt('hello.txt', arr, fmt='%1.3f')

print("file saved")


Example: Setting the fmt option in numpy.savetxt()

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