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In Fortran, I can use:

open(10, file = 'output')
write(10, '(5A10)') 'apple', 'banana', 'orange', 'grape', 'berry'

Is there a similar way in Python of writing the output?

I know I can use:

f.write('%5s\t%5s\t%5s\t%5s\t%5s' % ('apple', 'banana', 'orange', 'grape', 'berry'))

But how can I make it more compact? Using a similar way of '(5A10)', instead of the lengthy '%5s\t%5s\t%5s\t%5s\t%5s'.

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4
  • You can try storing it as a tuple, say t, and use f.write(*t). Commented Mar 13, 2016 at 23:07
  • It's not just Fortran 90 where you can do this ... This formatting goes back to at least Fortran 77. I never really dug into the F66 standard well enough to know whether you could do it portably there... Commented Mar 13, 2016 at 23:13
  • note modern fortran supports a variable multiplier: write(10,'(*(a10))') so you don't need to hard code the list length. I don't think there is a nice way to do that in python. Commented Mar 14, 2016 at 15:16
  • @agentp: Great tip! Works like a charm. Thanks a lot! I should ask more questions in Stack Overflow. People here are like genius! Lol Commented Mar 16, 2016 at 6:34

2 Answers 2

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7

You can use fortranformat: https://pypi.python.org/pypi/fortranformat

Works great!

>>> import fortranformat as ff
>>> header_line = ff.FortranRecordWriter('(A15, A15, A15)')
>>> header_line.write(['x', 'y', 'z'])
  '              x              y              z'
>>> line = FortranRecordWriter('(3F15.3)')
>>> line.write([1.0, 0.0, 0.5])
  '          1.000          0.000          0.500'
>>> line.write([1.1, 0.1, 0.6])
  '          1.100          0.100          0.600'
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'line' is string, so, you can print or write to a file.
3

No, there's no real shortcut here. In this case, you might try:

file_handle.write('\t'.join('%s' % f for f in fruits))

I'm not sure that this ends up being much more compact until fruits gets a little longer, but I think that it does make the output a little more obvious...

Also, if I'm reading your format statement correctly (it's been 2 years since I've spend much time with Fortran), you are formatting 5 strings with each 10 characters wide. The corresponding python format code for a string that is 10 characters wide is '%10.10s' (10 characters minimum, 10 characters maximum width). In that case, the tabs are unnecessary and you could write it as:

>>> fruits = ('apple', 'banana', 'orange', 'grape', 'berry')
>>> (5*'%10.10s') % fruits
'     apple    banana    orange     grape     berry'

Which isn't too much more verbose than the fortran way.

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4 Comments

OK. Because the data I am dealing with has a varying column. The fortran format writing is more easier to deal with. I will use f.write('%s' % ('apple\tbanana\torange\tgrape\tberry')) for now. But I just learnt a new way of writing output in Python from you. Already keep a note for this :)
@JianliCheng -- '%s' % 'some_string' is the same thing as some_string. No need to do formatting in that case :-)
The 5*'%10.10s' trick is exactly what I am looking for. Thank you so much. But what if some elements in my array are integers or floats? In fortran, I can do '(2A4, 3I4)', which write 2 strings with 4 characters and 3 integers with 4 characters.
'2 * '%4.4s' + 3 * '%4.4d' is one option. This will 0-pad the integers. If you don't want them 0-padded (as I don't think they will be in fortran with that format statement), then you could just do 5 * '%4.4s' as the format statement.

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