NumPy Input and Output: savez() function

Last update on August 19 2022 21:50:38 (UTC/GMT +8 hours)

numpy.savez() function

The savez() function is used to save several arrays into a single file in uncompressed .npz format.

If arguments are passed in with no keywords, the corresponding variable names, in the .npz file, are ‘arr_0’, ‘arr_1’, etc.
If keyword arguments are given, the corresponding variable names, in the .npz file will match the keyword names.

Syntax:

numpy.savez(file, *args, **kwds)

Version: 1.15.0

Parameter:

Name	Description	Required / Optional
file	Either the file name (string) or an open file (file-like object) where the data will be saved. If file is a string or a Path, the .npz extension will be appended to the file name if it is not already there. str or file	Required
args	Arrays to save to the file. Since it is not possible for Python to know the names of the arrays outside savez, the arrays will be saved with names “arr_0”, “arr_1”, and so on. These arguments can be any expression. Arguments	Optional
kwds	Arrays to save to the file. Arrays will be saved in the file with the keyword names. Keyword arguments	Optional

Returns: None

Notes:
The .npz file format is a zipped archive of files named after the variables they contain.
The archive is not compressed and each file in the archive contains one variable in .npy format.

When opening the saved .npz file with load a NpzFile object is returned.
This is a dictionary-like object which can be queried for its list of arrays (with the .files attribute),and for the arrays themselves.

NumPy.savez() method Example-1:

Using savez with *args, the arrays are saved with default names.

>>> import numpy as np
>>> from tempfile import TemporaryFile
>>> outfile = TemporaryFile()
>>> a = np.arange(12)
>>> b = np.sin(a)
>>> np.savez(outfile, a, b)
>>> outfile.seek(0) # Only needed here to simulate closing & reopening file
>>> npzfile = np.load(outfile)
>>> npzfile.files

Output:

['arr_1', 'arr_0']

>>> import numpy as np
>>> from tempfile import TemporaryFile
>>> outfile = TemporaryFile()
>>> a = np.arange(12)
>>> b = np.sin(a)
>>> np.savez(outfile, a, b)
>>> outfile.seek(0) # Only needed here to simulate closing & reopening file
>>> npzfile = np.load(outfile)
>>> npzfile['arr_0']

Output:

array([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11])

>>> import numpy as np
>>> from tempfile import TemporaryFile
>>> outfile = TemporaryFile()
>>> a = np.arange(12)
>>> b = np.sin(a)
>>> np.savez(outfile, a, b)
>>> outfile.seek(0) # Only needed here to simulate closing & reopening file
>>> npzfile = np.load(outfile)
>>> npzfile['arr_1']

Output:

array([ 0.        ,  0.84147098,  0.90929743,  0.14112001, -0.7568025 ,
       -0.95892427, -0.2794155 ,  0.6569866 ,  0.98935825,  0.41211849,
       -0.54402111, -0.99999021])

NumPy.savez() method Example-2:

Using savez with **kwds, the arrays are saved with the keyword names.

>>> import numpy as np
>>> from tempfile import TemporaryFile
>>> outfile = TemporaryFile()
>>> a = np.arange(12)
>>> b = np.sin(a)
>>> outfile = TemporaryFile()
>>> np.savez(outfile, a=a, b=b)
>>> outfile.seek(0)
>>> npzfile = np.load(outfile)
>>> npzfile.files

Output:

['a', 'b']

>>> import numpy as np
>>> from tempfile import TemporaryFile
>>> outfile = TemporaryFile()
>>> a = np.arange(12)
>>> b = np.sin(a)
>>> outfile = TemporaryFile()
>>> np.savez(outfile, a=a, b=b)
>>> outfile.seek(0)
>>> npzfile = np.load(outfile)
>>> npzfile['a']

Output:

array([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11])

>>> import numpy as np
>>> from tempfile import TemporaryFile
>>> outfile = TemporaryFile()
>>> a = np.arange(12)
>>> b = np.sin(a)
>>> outfile = TemporaryFile()
>>> np.savez(outfile, a=a, b=b)
>>> outfile.seek(0)
>>> npzfile = np.load(outfile)
>>> npzfile['b']

Output:

array([ 0.        ,  0.84147098,  0.90929743,  0.14112001, -0.7568025 ,
       -0.95892427, -0.2794155 ,  0.6569866 ,  0.98935825,  0.41211849,
       -0.54402111, -0.99999021])

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