CS61A: Miscellaneous Python Features

Overview

• Operators
• Multiple Return Values
• Docstrings
• Doctests
• Default Arguments

Operators

• Shorthand notation for calling builtin functions.

from operator import add, mul

(2+3*4+5) == add(add(2,mul(3,4)),5) # These are equivalent

True

Division (/ and //)

• Two types of division: True Division and Integer Division
  • True Division (/,truediv()): Mathematically accurate, returns answer in a float.
  • Integer Division (//,floordiv()): Returns the number of time the divisor multiplies into the dividend. In other words, it returns the answer in an integer, truncated.

from operator import truediv, floordiv
print(2013 / 10 == truediv(2013,10))
print(2013 // 10 == floordiv(2013,10))

True
True

Modulus (%)

• Returns an integer remainder, the remainder of the division operation.

from operator import mod
2013 % 10 == mod(2013,10)

True

Multiple Return Values

• A function can return multiple values. Split the remainder into two values with a comma.

def divide_exact(n,d):
    return n // d, n % d

quotient, remainder = divide_exact(2024,10)
print(quotient, remainder)

202 4

• If we execute a python file with the -i flag, we are able to enter interactive mode, which gives us a python interpreter shell containing all the code that was defined in the source file.

Docstrings

• 61A convention: formal parameters are capitalized in the docstrings

Doctest

• Doctests are a string demonstrating how the function would behave when ran.
  • It emulates the interpreter environment.
• We can simulate the doc tests with the python3 -m doctest -v <filename> command.
  • If successful, nothing happens
  • If not, error
  • We can also add the -v flag after the doctest option to see more verbose information.
• The -m doctest essentially runs the python file with the doctest module.

Default Values

• We can use the assignment operator = to assign a default value to a function.
  • If we call the function without defining that value, it will use the default value instead. We keep them towards the end as any arguments are automatically applied to the front arguments.

def divide_exact(n=2024,d=10):
    """Returns the quotient and remainder of dividing N by D.
    >>> q, r = divide_exact(2024, 10)
    >>> q
    202
    >>> r
    3
    """ 
    return n // d, n % d