I have a variable, abc, defined as 'batting_stats' and want to run a line of code that is 'pyb.batting_stats(2020)'. I want to use string syntax to create the line by joining abc with 'pyb.' and '(2020)' and then run that line of code - how can I do this? I seem to be creating a larger string instance rather than a runnable line of code. Cheers!

CodePudding user response：

You probably don't want to do this; it's possible, but in the vast majority of circumstances, it's a bad idea.

Options:

• If possible, try to rewrite the code so you don't need to look up by name at all; for instance, you could change the other code so that it stores pyb.batting_stats as a function rather than as a string

  abc = pyb.batting_stats  # note no brackets
  
  # later
  result = abc(2020)
  

• If you do need to look up by name, you can use getattr, like this:

  # At the top of the script
  ALLOWED_NAMES = ['batting_stats', ...]
  
  # in the code where you need it
  if abc not in ALLOWED_NAMES:
      raise ValueError("Invalid name passed: %s" % abc)
  result = getattr(pyb, abc)(2020)
  

• Probably a better way would be to use a dictionary as a dispatch table:

  dispatch_table = {
       'batting_stats': pyb.batting_stats,
       ...: ...,
  }
  result = dispatch_table[abc](2020)
  

  This automatically raises an exception if an unexpected name is passed.

  It also has the benefit that you can use a different string in the abc variable than the method name; for example, if you need to rename the function but maintain the names in an API or vice versa:

  dispatch_table = {
       'battingstats': pyb.batting_stats,  # legacy name
       'batting_stats': pyb.batting_stats,
       ...: ...,
  }
  result = dispatch_table[abc](2020)
  

• If you absolutely must run a piece of code from a string, you can use the eval or exec builtin functions; however, it's almost always a bad idea.

  Use of eval and exec is so frequently dangerous and insecure (Common Weakness #95) that it's better to avoid it altogether. Luckily, at least in Python, there's almost always an alternative; moreover, those alternatives are typically cleaner, more flexible, faster to run and easier to debug. Cases where there's no alternative are vanishingly rare.

CodePudding user response：

There are two ways so get this answer.

First you can try something like

os.system(f'pyb.{abc}(2020)')

or

exec('print("hi")')

If you want to store the output try this