Build the full path filename in Python

Question

I need to pass a file path name to a module   How do I build the file path from a directory name  base filename  and a file format string   The directory may or may not exist at the time of call   For example   dir name   home me dev my reports  base filename  daily report  format    pdf    I need to create a string   home me dev my reports daily report pdf    Concatenating the pieces manually doesn t seem to be a good way  I tried os path join   join dir name base filename format    but it gives   home me dev my reports daily report pdf

User · Answer

Just use os path join to join your path with the filename and extension  Use sys argv to access arguments passed to the script when executing it      usr bin env python3   coding  utf-8    import netCDF4 as nc import numpy as np import numpy ma as ma import csv as csv  import os path import sys  basedir     data reu data soil moisture   suffix    nc    def read fid filename       fid   nc MFDataset filename  r       fid close       return fid  def read var file  varname       fid   nc Dataset file   r       out   fid variables varname         fid close       return out   if   name         main         if len sys argv   lt  2          print  Please specify a year        else          filename   os path join basedir      join  sys argv 1   suffix            time   read var ncf   time           lat   read var ncf   lat           lon   read var ncf   lon           soil   read var ncf   soilw     Simply run the script like        on windows-based systems    python script py year       on unix-based systems      script py year

User · Answer

This works fine  os path join dir name  base filename    quot   quot    filename suffix   Keep in mind that os path join   exists only because different operating systems use different path separator characters  It smooths over that difference so cross-platform code doesn t have to be cluttered with special cases for each OS  There is no need to do this for file name  quot extensions quot   see footnote  because they are always connected to the rest of the name with a dot character  on every OS  If using a function anyway makes you feel better  and you like needlessly complicating your code   you can do this  os path join dir name      join  base filename  filename suffix     If you prefer to keep your code clean  simply include the dot in the suffix  suffix     pdf  os path join dir name  base filename   suffix   That approach also happens to be compatible with the suffix conventions in pathlib  which was introduced in python 3 4 after this question was asked  New code that doesn t require backward compatibility can do this  suffix     pdf  pathlib PurePath dir name  base filename   suffix   You might prefer the shorter Path instead of PurePath if you re only handling paths for the local OS  Warning  Do not use pathlib s with suffix   for this purpose  That method will corrupt base filename if it ever contains a dot   Footnote  Outside of Micorsoft operating systems  there is no such thing as a file name  quot extension quot   Its presence on Windows comes from MS-DOS and FAT  which borrowed it from CP M  which has been dead for decades  That dot-plus-three-letters that many of us are accustomed to seeing is just part of the file name on every other modern OS  where it has no built-in meaning

User · Answer

Um  why not just    gt  gt  gt  gt  import os  gt  gt  gt  gt  os path join dir name  base filename         format    home me dev my reports daily report pdf

User · Answer

If you are fortunate enough to be running Python 3 4   you can use pathlib    gt  gt  gt  from pathlib import Path  gt  gt  gt  dirname     home reports   gt  gt  gt  filename    daily   gt  gt  gt  suffix     pdf   gt  gt  gt  Path dirname  filename  with suffix suffix  PosixPath   home reports daily pdf

[python] Build the full path filename in Python

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