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!

Neonatal

I guess modifying your Fortran programs is not an option ? – Estrada

@HP Mark: not an option. – Neonatal

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 :-) – Estrada

Answer 1

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

Devoirs

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

Answer 2

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

Carnallite

I've been putting off numpy for a long time... maybe it's time I reconsider. Thank you! (+1) – Neonatal

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. – Putt

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

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 . – Forgotten

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

Answer 3

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).

Pyelonephritis