1. Fundamentals of Programming I Default and Optional Parameters
Computer Science 111
Fundamentals of Programming I
Default and Optional Parameters

2. Arguments and Return Values
A function can receive data (arguments) from its caller
A function can return a single value to its caller
y = math.sqrt(x)

3. Why Use Parameters?
Parameters allow a function to be used with different data in different parts of a program
The general method or algorithm is the same, but the arguments vary with the situation
>>> math.sqrt(2)
>>> math.sqrt(16)
4.0
>>>

4. Default and Optional Parameters
One or more parameters can have default values, so the caller can omit some arguments
>>> round(3.1416) # Default precision is 0 3
>>> round(3.1416, 3)
3.142
>>> list(range(5)) # Default lower bound is 0, and
[0,1,2,3,4] # default step value is 1
>>> list(range(1, 5))
[1,2,3,4]
>>> list(range(1, 5, 2))
[1,3]

5. Convert Based Numbers to ints
Write a general function that expects a string representation of a number and its base (an int) as arguments
The function returns the integer represented
>>> repToInt('10', 2) # 102 = 2 2
>>> repToInt('10', 10) # 1010 = 10 10
>>> repToInt('10', 16) # 1016 = 16 16
>>> repToInt('100', 2) # 1002 = 4

6. Implementation def repToInt(digits, base):
"""Returns the integer represented by the digits
in the given base."""
intValue = 0
expo = len(digits – 1)
for ch in digits:
ch = string.upper(ch)
intvalue += hexdigits[ch] * base ** expo
expo -= 1
return intValue

7. Default and Optional Parameters
One or more parameters can have default values, so the caller can omit some arguments
>>> repToInt('111', 2) 7
>>> repToInt('111', 10)
111
>>> repToInt('111', 16)
273
>>> repToInt('111') # Same result as the previous line
The caller can treat base16 as the standard base in this system or use other bases by mentioning them

8. Implementation def repToInt(digits, base = 16):
"""Returns the integer represented by the digits
in the given base."""
intValue = 0
expo = len(digits – 1)
for ch in digits:
ch = string.upper(ch)
intvalue += hexdigits[ch] * base ** expo
expo -= 1
return intValue

9. Some Syntax Rules
The required arguments used in a function call must match the required parameters named in the definition, by position
The programmer should list the required parameters first (to the left) in the function’s definition
def <function name>(<required params>, <default params>):

10. Some Syntax Rules A required parameter is just a name
A default parameter looks like an assignment statement
def <function name>(<name>,…, <name> = <expression>,…):

11. Section 6.6 Higher-Order Functions
For Wednesday
Section 6.6
Higher-Order Functions