numpy.savetxt(fname, X, fmt='%.18e', delimiter=' ')

Save an array to a text file.


fname : filename or file handle

If the filename ends in .gz, the file is automatically saved in compressed gzip format. loadtxt understands gzipped files transparently.

X : array_like

Data to be saved to a text file.

fmt : str or sequence of strs

A single format (%10.5f), a sequence of formats, or a multi-format string, e.g. ‘Iteration %d – %10.5f’, in which case delimiter is ignored.

delimiter : str

Character separating columns.

See also

Save an array to a binary file in NumPy .npy format
Save several arrays into a .npz compressed archive


Further explanation of the fmt parameter (%[flag]width[.precision]specifier):


- : left justify

+ : Forces to preceed result with + or -.

0 : Left pad the number with zeros instead of space (see width).

Minimum number of characters to be printed. The value is not truncated if it has more characters.
  • For integer specifiers (eg. d,i,o,x), the minimum number of digits.
  • For e, E and f specifiers, the number of digits to print after the decimal point.
  • For g and G, the maximum number of significant digits.
  • For s, the maximum number of characters.

c : character

d or i : signed decimal integer

e or E : scientific notation with e or E.

f : decimal floating point

g,G : use the shorter of e,E or f

o : signed octal

s : string of characters

u : unsigned decimal integer

x,X : unsigned hexadecimal integer

This explanation of fmt is not complete, for an exhaustive specification see [R268].


[R268](1, 2) Format Specification Mini-Language, Python Documentation.


>>> savetxt('test.out', x, delimiter=',')   # X is an array
>>> savetxt('test.out', (x,y,z))   # x,y,z equal sized 1D arrays
>>> savetxt('test.out', x, fmt='%1.4e')   # use exponential notation

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