# Audience:
#   - has programmed
#   - perhaps in python

# Agenda:
# 
# - working in python with idle or emacs
#   - version / download
#   - repl vs. file
#   - syntax errors
#   - errors with backtraces
# 
# - accomplishing things
#   - basic data types
#   - names
#   - functions and scope
#   - assert
#   - recursion
#   - break vs. return vs. exception
#   - classes
#   - lists
#     - indexing
#     - copying
#   - dictionaries
#   - list comprehensions (map&filter)
#
# - common gotchas
#   - whitespace
#   - print vs. return
#   - magical helpfulness
#   - integer division
#   - floating point precision
#   - copy/paste
#   - aliasing
#   - tuples and parentheses


3
3 + 2  # have numbers
13 - 2 * 4 # they do what you expect
(13 - 2) * 4 # you can use parentheses to indicate precedence, as usual
8 / 2 # division is exact, like in C
8 / 2.0 # unless you specify otherwise
7 % 3 # modulo, etc.
3.0 == 3 # equality is not stupid


"hi" # have strings
"pin" + "to" # can add them to concatenate
3 * "pin" # can multiply them to repeat
'pin' * 3 # single quotes okay.

3 < 5 # have booleans
5 < 3

type(3) == int # types are first class objects



# Names and Scope

a = 3
a = 5
b = a
a = 10
b #?

# multiple assignment
(a, b) = [1, 2]
a
b


# Functions: my favorite datatype

def plus_one(a):
    return a + 1

# whitespace sensitive

def plus(a, b):
    return a + b


def plus_ten(a):
    b = a + 10
    return b
a = 5
b = 3
c = 7
d = plus_ten(c)
a #?
b #?
c #?
d #?


# if x = 1

# interactive model: syntax errors
# interactive model: variable completion

def near(a, b, tolerance=0.1):
    return abs(a - b) < tolerance

def is_even(n):
    return n % 2 == 0

def assert_equal(expected, observed, message=""):
    assert expected == observed, ("Expected [%s] but found [%s]: %s" %
                                  (expected, observed, message))
    print "ok."

# recursion

def integer_times(a, b):
    # todo: check that it's an integer
    if b == 0: # base case:
        return 0
    else: # recursive step:
        return a + integer_times(a, b-1)


''' #RESET
    elif b < 0:
        return integer_times(-a, -b)
'''

def test_integer_times():
    assert_equal(1, integer_times(1,1))
    assert_equal(0, integer_times(1,0))
    assert_equal(0, integer_times(0,1))
    assert_equal(6, integer_times(2,3))
    assert_equal(-6, integer_times(-2,3))
    assert_equal(-6, integer_times(2,-3))
    assert_equal(6, integer_times(-2,-3))

test_integer_times()     # RESET


def is_prime(n):
    result = False
    for divisor in range(2,math.sqrt(n)):
        if n % divisor == 0:
            result = True
            break # breaks out of nearest for or while
    return result




def fibonacci(n):
    if "something about n": #base case
        return "what base value?"
    else:
        return "what result of a recursive step?"