Argparse optional positional arguments

Question

I have a script which is meant to be used like this  usage  installer py dir  -h   -v   dir is a positional argument which is defined like this   parser add argument  dir   default os getcwd      I want the dir to be optional  when it s not specified it should just be cwd   Unfortunately when I don t specify the dir argument  I get Error  Too few arguments

User · Accepted Answer

Use nargs      or nargs     if you need more than one dir  parser add argument  dir   nargs      default os getcwd     extended example   gt  gt  gt  import os  argparse  gt  gt  gt  parser   argparse ArgumentParser    gt  gt  gt  parser add argument  -v   action  store true    StoreTrueAction option strings   -v    dest  v   nargs 0  const True  default False  type None  choices None  help None  metavar None   gt  gt  gt  parser add argument  dir   nargs      default os getcwd     StoreAction option strings     dest  dir   nargs      const None  default   home vinay   type None  choices None  help None  metavar None   gt  gt  gt  parser parse args  somedir -v  split    Namespace dir  somedir   v True   gt  gt  gt  parser parse args  -v  split    Namespace dir   home vinay   v True   gt  gt  gt  parser parse args    split    Namespace dir   home vinay   v False   gt  gt  gt  parser parse args   somedir    Namespace dir  somedir   v False   gt  gt  gt  parser parse args  somedir -h -v  split    usage   -h   -v   dir   positional arguments    dir  optional arguments    -h  --help  show this help message and exit   -v

User · Answer

As an extension to  VinaySajip answer  There are additional nargs worth mentioning    parser add argument  dir   nargs 1  default os getcwd       N  an integer   N arguments from the command line will be gathered together into a list   parser add argument  dir   nargs      default os getcwd            All command-line arguments present are gathered into a list  Note that it generally doesn t make much sense to have more than one positional argument with nargs      but multiple optional arguments with nargs     is possible    parser add argument  dir   nargs      default os getcwd           Just like      all command-line args present are gathered into a list  Additionally  an error message will be generated if there wasn   t at least one command-line argument present    parser add argument  dir   nargs argparse REMAINDER  default os getcwd      argparse REMAINDER  All the remaining command-line arguments are gathered into a list  This is commonly useful for command line utilities that dispatch to other command line utilities  If the nargs keyword argument is not provided  the number of arguments consumed is determined by the action  Generally this means a single command-line argument will be consumed and a single item  not a list  will be produced   Edit  copied from a comment by  Acumenus  nargs     The docs say       One argument will be consumed from the command line if possible and produced as a single item  If no command-line argument is present  the value from default will be produced

User · Answer

parser add argument also has a switch required  You can use required False  Here is a sample snippet with Python 2 7   parser   argparse ArgumentParser description  get dir   parser add argument  --dir   type str  help  dir   default os getcwd    required False  args   parser parse args

[python] Argparse optional positional arguments?

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