Python 2.7: how to append lines which contain both string & numeric values to text file?

Question

I want to append following line to my text file:

Degree of polarization is 8.23 % and EVPA is 45.03 degree.

i.e. I want both string and numeric values to be appended.

I want to append above line with different numeric values after each run of my python code.

Any help will be appreciated.

For example

>>> a = 10.5 
>>> with open("myfile.txt","a") as f:
...  f.write(a)

gives me error.

Please do read the Python tutorial before asking basic questions like these. String formatting for output is [covered in a dedicated chapter](https://docs.python.org/2/tutorial/inputoutput.html). — Martijn Pieters, Aug 13 '15 at 07:15
@MartijnPieters: Please do read carefully before giving your comment. I am asking not about string formating. My question is related to appending. — atom, Aug 13 '15 at 07:33
possible duplicate of [How do you append to a file in Python?](http://stackoverflow.com/questions/4706499/how-do-you-append-to-a-file-in-python) — Peter Wood, Aug 13 '15 at 07:42
I want to try with open("myfile.txt","a") as f: What should be next code line? What does f.write() will contain ? — atom, Aug 13 '15 at 07:42
@atom: the tutorial still answers your question. Why not read that carefully? — Martijn Pieters, Aug 13 '15 at 07:50
@atom What error are you dealing with? I imagine it's that you can't write a float to the file. You have to convert it to a string first, which is what my answer below is telling you. — Peter Wood, Aug 13 '15 at 07:53

VRage · Accepted Answer · 2015-08-13T07:54:03.297

3

Do you mean something like this:

while True:
    polarization = getPolarization()
    evpa = getEvpa()
    my_text = "Degree of polarization is {} % and EVPA is {} degree.".format(polarization, evpa)

    with open("test.txt", "a") as myfile:
        myfile.write(my_text)

Maybe you should also write what have you tried yet and what problems/errors occurred

edited Aug 13 '15 at 07:54

answered Aug 13 '15 at 07:48

VRage

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Peter Wood · Answer 2 · 2015-08-13T08:11:46.420

0

You can only write strings to files.

Strings can be concatenated:

>>> 'a' + 'b'
'ab'

Numbers can be converted to strings:

>>> str(4)
'4'

>>> str(5.6)
'5.6'

You should be able to get started with that.

Also, Python's string formatting will automatically do this for you:

>>> '{} % and {} degree'.format(6.7, 8.9)
'6.7 % and 8.9 degree'

Or with a more readable format using keywords:

>>> '{polarization} % and {evpa} degree'.format(polarization=6.7, evpa=8.9)
'6.7 % and 8.9 degree'

edited Aug 13 '15 at 08:11

answered Aug 13 '15 at 07:25

Peter Wood

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My question is NOT related to string formating. It is related to appending lines to text file. – atom Aug 13 '15 at 07:35
You can only write strings to files so you need to convert the values first. Your question isn't particularly clear. What difficulty do you have? – Peter Wood Aug 13 '15 at 07:39

Python 2.7: how to append lines which contain both string & numeric values to text file?

2 Answers2