CODEWITHSUNDEEP
pythonstringmultiline
sdaau
sdaau

Reputation: 38619

Converting between multiline and single-line (with escaped linebreaks) string representations in Python?

Let's say I have a multiline string in Python; I would like to convert it to a single-line representation, where the line endings are written as \n escapes (and tabs as \t etc) - say, in order to use it as some command line argument. So far, I figured that pprint.pformat can be used for the purpose - but the problem is, I cannot convert from this single-line representation back to a "proper" multi-line string; here's an example:

import string
import pprint

MYSTRTEMP = """Hello $FNAME!

I am writing this.

Just to test.
"""

print("--Testing multiline:")

print(MYSTRTEMP)

print("--Testing single-line (escaped) representation:")

testsingle = pprint.pformat(MYSTRTEMP)
print(testsingle)

# http://stackoverflow.com/questions/12768107/string-substitutions-using-templates-in-python
MYSTR = string.Template(testsingle).substitute({'FNAME': 'Bobby'})

print("--Testing single-line replaced:")
print(MYSTR)

print("--Testing going back to multiline - cannot:")
print("%s"%(MYSTR))

This example with Python 2.7 outputs:

$ python test.py
--Testing multiline:
Hello $FNAME!

I am writing this.

Just to test.

--Testing single-line (escaped) representation:
'Hello $FNAME!\n\nI am writing this.\n\nJust to test.\n'
--Testing single-line replaced:
'Hello Bobby!\n\nI am writing this.\n\nJust to test.\n'
--Testing going back to multiline - cannot:
'Hello Bobby!\n\nI am writing this.\n\nJust to test.\n'

One problem is that the single-line representation seems to include the ' single quotes in the string itself - second problem is that I cannot go back from this representation back to a proper multiline string.

Is there a standard method in Python to achieve this, such that - as in the example - I could go from multi-line to escaped single-line, then do templating, then convert the templated single-line back to a multi-line representation?

Upvotes: 0

Views: 1611

Answers (1)

univerio
univerio

Reputation: 20518

To go from the repr of a string (which is what pformat gives you for a string) to the actual string, you can use ast.literal_eval:

>>> repr(MYSTRTEMP)
"'Hello $FNAME!\\n\\nI am writing this.\\n\\nJust to test.\\n'"
>>> ast.literal_eval(repr(MYSTRTEMP))
'Hello $FNAME!\n\nI am writing this.\n\nJust to test.\n'

Converting to repr just to convert back is probably not a good way to accomplish your original goal, though, but this is how you would do it.

Upvotes: 2

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