When defining a function in Python, you can specify default values for parameters. For example, here is the example from the previous section, modified to supply a default count of 1 if no count is specified:

def print_HL7_delimiter(fieldlevel, count=1):
	if fieldlevel == 0:
		print "|" * count
	elif fieldlevel == 1:
		print "^" * count
	elif fieldlevel == 2:
		print "&" * count

print_HL7_delimiter(1)
print_HL7_delimiter(1, 3)	

The output for this code is:

^
^^^

Here, the count parameter has a default value of 1. This is the value that is used if no value is supplied for this parameter, as in the first call to print_HL7_delimiter(). If a value is explicitly specified for the count parameter - as in the second call to print_HL7_delimiter() - the value overrides the default value.

If you have more than one parameter for which you have specified a default, and you want to override the default values for some of the parameters but not others, you can provide parameter names as part of the function call. For example:

def print_with_delimiters(text, opening_delimiter="|", closing_delimiter="|"):
        print opening_delimiter + text + closing_delimiter

print_with_delimiters("XYZ_HOSPITAL")
print_with_delimiters("XYZ_HOSPITAL", "^")
print_with_delimiters("XYZ_HOSPITAL", closing_delimiter="^")

In the third call to print_with_delimiters(), a value is supplied for the closing_delimiter parameter, overriding the default. The default value of opening_delimiter is left untouched. The output for this code is:

|XYZ_HOSPITAL|
^XYZ_HOSPITAL|
|XYZ_HOSPITAL^

	If you specify a default for a parameter, you must specify defaults for all parameters that follow it in the function definition. Here is an example of a function definition that is illegal in Python: def print_with_delimiters(text, opening_delimiter="|", closing_delimiter): print opening_delimiter + text + closing_delimiter Here, opening_delimiter has a default but closing_delimiter does not. Python does not allow this.