import shelve
import os.path

def savevars(*args):
	"""
	SAVEVARS - function to save variables to a file.

	This function saves one or more variables to a file.  The names of the variables
	must be supplied.  If more than one variable is specified, it may be done with
	lists of names and values or a dictionary of name:value pairs.  All the variables
	in the workspace may be saved by specifying the globals() dictionary, but this
	may include a lot of extraneous data.

	Usage:
	   savevars('shelve.dat','a',a)
	   savevars('shelve.dat',['a','b'],[a,b])
	   savevars('shelve.dat',{'a':a,'b':b})
	   savevars('shelve.dat',globals())

	"""

	filename=''
	nvdict={}

	if len(args) >= 1 and isinstance(args[0],str):
		filename=args[0]
		if not filename:
			filename='/tmp/shelve.dat'

	else:
		raise TypeError("Missing file name.")

	if   len(args) >= 3 and isinstance(args[1],str):    # (filename,name,value)
		for i in range(1,len(args),2):
			nvdict[args[i]]=args[i+1]

	elif len(args) == 3 and isinstance(args[1],list) and isinstance(args[2],list):    # (filename,[names],[values])
		for name,value in zip(args[1],args[2]):
			nvdict[name]=value

	elif len(args) == 2 and isinstance(args[1],dict):    # (filename,{names:values})
		nvdict=args[1]

	else:
		raise TypeError("Unrecognized input arguments.")

	if os.path.exists(filename):
		print(("Shelving variables to existing file '%s'." % filename))
	else:
		print(("Shelving variables to new file '%s'." % filename))

	my_shelf = shelve.open(filename,'c') # 'c' for create if not exist, else 'n' for new

	for name,value in list(nvdict.items()):
		try:
			my_shelf[name] = value
			print(("Variable '%s' shelved." % name))
		except TypeError:
			print(("Variable '%s' not shelved." % name))

	my_shelf.close()