How to implement the --verbose or -v option into a script

Question

I know the --verbose or -v from several tools and I d like to implement this into some of my own scripts and tools   I thought of placing   if verbose      print       through my source code  so that if a user passes the -v option  the variable verbose will be set to True and the text will be printed   Is this the right approach or is there a more common way   Addition  I am not asking for a way to implement the parsing of arguments  That I know how it is done  I am only interested specially in the verbose option

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Building and simplifying  kindall s answer  here s what I typically use   v print   None def main       parser   argparse ArgumentParser       parser add argument  -v    --verbosity   action  count                            help  increase output verbosity  e g   -vv is more than -v         args   parser parse args        if args verbosity          def  v print  verb args               if verb args 0   gt   3 - args verbosity                   print verb args 1        else           v print   lambda  a  None    do-nothing function      global v print     v print    v print  if   name         main         main     This then provides the following usage throughout your script   v print 1   INFO message   v print 2   WARN message   v print 3   ERROR message     And your script can be called like this     python verbose-tester py -v ERROR message    python verbose tester py -vv WARN message ERROR message    python verbose-tester py -vvv INFO message WARN message ERROR message   A couple notes    Your first argument is your error level  and the second is your message  It has the magic number of 3 that sets the upper bound for your logging  but I accept that as a compromise for simplicity  If you want v print to work throughout your program  you have to do the junk with the global  It s no fun  but I challenge somebody to find a better way

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kindall s solution does not work with my Python version 3 5   styles correctly states in his comment that the reason is the additional optional keywords argument  Hence my slightly refined version for Python 3 looks like this   if VERBOSE      def verboseprint  args    kwargs           print  args    kwargs  else      verboseprint   lambda  a    k  None   do-nothing function

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It might be cleaner if you have a function  say called vprint  that checks the verbose flag for you  Then you just call your own vprint function any place you want optional verbosity

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There could be a global variable  likely set with argparse from sys argv  that stands for whether the program should be verbose or not  Then a decorator could be written such that if verbosity was on  then the standard input would be diverted into the null device as long as the function were to run   import os from contextlib import redirect stdout verbose   False  def louder f       def loud f  args    kwargs           if not verbose              with open os devnull   w   as void                  with redirect stdout void                       return f  args    kwargs          return f  args    kwargs      return loud f   louder def foo s       print s 3   foo  bar     This answer is inspired by this code  actually  I was going to just use it as a module in my program  but I got errors I couldn t understand  so  I adapted a portion of it   The downside of this solution is that verbosity is binary  unlike with logging  which allows for finer-tuning of how verbose the program can be  Also  all print calls are diverted  which might be unwanted for

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What I need is a function which prints an object  obj   but only if global variable verbose is true  else it does nothing   I want to be able to change the global parameter  verbose  at any time  Simplicity and readability to me are of paramount importance  So I would proceed as the following lines indicate   ak HP2000    python3 Python 3 4 3  default  Oct 14 2015  20 28 29    GCC 4 8 4  on linux Type  help    copyright    credits  or  license  for more information   gt  gt  gt  verbose   True  gt  gt  gt  def vprint obj           if verbose              print obj          return       gt  gt  gt  vprint  Norm and I   Norm and I  gt  gt  gt  verbose   False  gt  gt  gt  vprint  I and Norm    gt  gt  gt     Global variable  verbose  can be set from the parameter list  too

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Use the logging module   import logging as log     args   p parse args   if args verbose      log basicConfig format    levelname s    message s   level log DEBUG      log info  Verbose output    else      log basicConfig format    levelname s    message s    log info  This should be verbose    log warning  This is a warning    log error  This is an error      All of these automatically go to stderr     python myprogram py WARNING  This is a warning  ERROR  This is an error     python myprogram py -v INFO  Verbose output  INFO  This should be verbose  WARNING  This is a warning  ERROR  This is an error    For more info  see the Python Docs and the tutorials

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I stole the logging code from virtualenv for a project of mine  Look in main   of virtualenv py to see how it s initialized  The code is sprinkled with logger notify    logger info    logger warn    and the like  Which methods actually emit output is determined by whether virtualenv was invoked with -v  -vv  -vvv  or -q

User · Answer

What I do in my scripts is check at runtime if the  verbose  option is set  and then set my logging level to debug  If it s not set  I set it to info  This way you don t have  if verbose  checks all over your code

User · Answer

My suggestion is to use a function  But rather than putting the if in the function  which you might be tempted to do  do it like this   if verbose      def verboseprint  args             Print each argument separately so caller doesn t need to           stuff everything to be printed into a single string         for arg in args             print arg          print else         verboseprint   lambda  a  None        do-nothing function    Yes  you can define a function in an if statement  and it ll only get defined if the condition is true    If you re using Python 3  where print is already a function  or if you re willing to use print as a function in 2 x using from   future   import print function  it s even simpler   verboseprint   print if verbose else lambda  a    k  None   This way  the function is defined as a do-nothing if verbose mode is off  using a lambda   instead of constantly testing the verbose flag    If the user could change the verbosity mode during the run of your program  this would be the wrong approach  you d need the if in the function   but since you re setting it with a command-line flag  you only need to make the decision once   You then use e g  verboseprint  look at all my verbosity    object    3  whenever you want to print a  verbose  message

[python] How to implement the --verbose or -v option into a script?

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