Python path-breaking script for use in R

Question

R does not support line continuation as Python, and it's disturbing to have long file paths like

/media/user/data/something-not-very-important-but-super-long/some-curious-secret-file.pdf

and can't break it into multiple lines.

The workaround is to use the file.path function:

file.path(
 "/root",
 "folder",
 "file.ods")

Manually editing is tedious, so here is a Python script that does the job for you:

#!/usr/bin/env python3
import sys
x = sys.argv[1]
# split by unix path separator
y = x.split("/")
# get rid of empty strings
y = [i for i in y if i]
# preserve / if it's an absolute path
if x.startswith("/"):
 y[0] = "/" + y[0]
# quote everything
y = ["'" + i + "'" for i in y]
res = "file.path(" + ",\n ".join(y) + ")"
print(res)

Answer 1

Always throw things in main:

def main():
 # code
main()

It might seem pointless but it does help with preventing global pollution, which is good if you ever decide to add a function somewhere.

Using

x = sys.argv[1]

is acceptable for a trivial script, but it's not much harder to use docopt and implement a proper command-line parser:

"""
Name Of Program.
Usage: prog.py <pathname>
"""
import docopt
def main():
 args = docopt.docopt(__doc__)
 x = args["<pathname>"]

Trivial, but it gives you --help, error reporting and sane handling of bad input, nearly for free.

This can be simplified a little with pathlib:

parts = pathlib.PurePosixPath(args["<pathname>"]).parts
if len(parts) >= 2 and parts[0] == "/":
 parts = ("/" + parts[1],) + parts[2:]

You can actually use just pathlib.Path but it may assume a Windows format on Windows machines.

Your quoting:

parts = ["'" + i + "'" for i in parts]

should be done with repr:

parts = map(repr, parts)

and the formatting should use .format:

res = "file.path({})".format(",\n ".join(parts))

This gives

#!/usr/bin/env python3
"""
Name Of Program.
Usage: prog.py <pathname>
"""
import docopt
import pathlib
def main():
 args = docopt.docopt(__doc__)
 parts = pathlib.PurePosixPath(args["<pathname>"]).parts
 if len(parts) >= 2 and parts[0] == "/":
 parts = ("/" + parts[1],) + parts[2:]
 args = ",\n ".join(map(repr, parts))
 print("file.path({})".format(args))
main()

Technically PEP 8 says docopt should be separated from pathlib, the second being in the stdlib, but it looks nicer this way for now.

Answer 2

This seems quite alright. I have a couple of tips though:

• Since you use the / in multiple places, it would be good to give it a name.

• The variable names could be improved: x and y don't tell much about what they are.

• Instead of "'" + i + "'", it's shorter and perhaps easier to read as "'%s'" % i, though the new style formatting is recommended, so this latter should be written as "'{}'".format(i)

Putting it together:

# use unix path separator
separator = '/'
origpath = sys.argv[1]
parts = origpath.split(separator)
# get rid of empty strings
parts = [item for item in parts if item]
# preserve / if it's an absolute path
if origpath.startswith(separator):
 parts[0] = separator + parts[0]
# quote everything
parts = ["'{}'".format(item) for item in parts]
res = "file.path(" + ",\n ".join(parts) + ")"
print(res)

• Veedrac: "Since you use the / in multiple places, it would be good to give it a name." Not sure I agree 'bout that. Also, new style formatting rulez: "'{}'".format(item).
• janos: @Veedrac replacing a magic string literal with a well-named variable is certainly a good thing. You seem to miss the point with the gist, which would only be marginally related if I had named the variable forward_slash. You're right about new style formatting though, updated that in my answer