Python scientific notation using D instead of E

Question

Some results file produced by Fortran programs report double precision numbers (in scientific notation) using the letter D instead of E, for instance:

1.2345D+02 # instead of 1.2345E+02

I need to process huge amounts of this data using Python, and I just realized it cannot read the numbers in the D notation, for instance:

>>> A = 1.0D+01 File "<stdin>", line 1 A = 1.0D+01 ^ SyntaxError: invalid syntax

Can I change my locale and let Python know that D means E? I really would not want to make a global search-and-replace!

I'd use sed to rip through the file and write it into the format your Python program wants. But then, I'd use sed for most programs anyway :-) — High Performance Mark
– High Performance Mark, Commented Dec 24, 2009 at 18:06

John Feminella · Accepted Answer · 2009-12-24 18:00:58Z

15

The simplest way, from your Python program, would be just to add a step before you interpret each entry:

>>> val = "1.5698D+03" # 1,569.8 >>> print float(val.replace('D', 'E')) 1569.8

answered Dec 24, 2009 at 18:00

John Feminella

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1 Comment

Escualo Over a year ago

I will accept this as the answer, but I'm sad Python does not have a better way to do this. Thanks!

Glorfindel · Accepted Answer · 2022-12-30 19:01:09Z

12

If you are dealing with lots of data and/or are doing a lot computations with that data, you might consider using the fortran-friendly numpy module which supports double-precision fortran format out of the box.

>>> numpy.float('1.5698D+03') 1569.8

edited Dec 30, 2022 at 19:01

Glorfindel

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answered Dec 24, 2009 at 18:31

Paul

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4 Comments

Mike T Over a year ago

On older versions of NumPy (e.g., 1.3.0) this raises a ValueError. I'm not sure what version of NumPy this was introduced.

talonmies Over a year ago

numpy version 1.80 still doesn't support this. Exactly what version of numpy was this?

JPaget Over a year ago

This appears to work only on older versions of Python on certain platforms. It doesn't work for Windows 7 64-bit/Python 2.7.9/numpy 1.9.2. See bugs.python.org/issue7919 .

Peter Erwin Over a year ago

It doesn't work for numpy version 1.15.3 (most recent as of 2018), either.

Glorfindel · Accepted Answer · 2022-12-30 19:01:19Z

Another option is the fortranformat library for Python. It will read strings and interpret them according to a FORTRAN format statement. i.e.

>>> import fortranformat as ff >>> line = ff.FortranRecordReader('(F10.0)') >>> line.read('1.5698D+03') [1569.8]

Install with easy_install -U fortranformat

Any questions, email me (I'm the author).

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