python and sys argv

Question

if len sys argv   lt  2      sys stderr write  Usage  sys argv 0         sys exit 1    if not os path exists sys argv 1        sys stderr write  ERROR  Database sys argv 1  was not found        sys exit 1    This is a portion of code I m working on  The first part I m trying to say if the user doesn t type python programname something then it will exit   The second part I m trying to see if the database exists  On both places I m unsure if I have the correct way to write out the sys argv s by stderr or not

User · Answer

I would do it this way   import sys  def main argv       if len argv   lt  2          sys stderr write  Usage   s  lt database gt      argv 0             return 1      if not os path exists argv 1            sys stderr write  ERROR  Database  r was not found      argv 1             return 1  if   name         main         sys exit main sys argv     This allows main   to be imported into other modules if desired  and simplifies debugging because you can choose what argv should be

User · Answer

BTW you can pass the error message directly to sys exit   if len sys argv   lt  2      sys exit  Usage   s database-name    sys argv 0    if not os path exists sys argv 1        sys exit  ERROR  Database  s was not found     sys argv 1

User · Answer

In Python  you can t just embed arbitrary Python expressions into literal strings and have it substitute the value of the string  You need to either   sys stderr write  Usage      sys argv 0     or  sys stderr write  Usage   s    sys argv 0     Also  you may want to consider using the following syntax of print  for Python earlier than 3 x    print  gt  gt sys stderr   Usage    sys argv 0    Using print arguably makes the code easier to read  Python automatically adds a space between arguments to the print statement  so there will be one space after the colon in the above example   In Python 3 x  you would use the print function   print  Usage    sys argv 0   file sys stderr    Finally  in Python 2 6 and later you can use  format   print  gt  gt sys stderr   Usage   0   format sys argv 0

[python] python and sys.argv

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