# Practical guidance
# bad
if sqrt(square(a) + square(b)) > 1:
    x = x + sqrt(square(a) + square(b))
# good
h = sqrt(square(a) + square(b))
if h > 1:
    x = x + h

# bad
x = (-b + sqrt(square(b) - 4 * a * c)) / (2 * a)
# good
disc_term = sqrt(square(b) - 4 * a * c)
x = (-b + disc_term) / (2 * a)

# ugly
def find_quadratic_root(a, b, c, plus=True):
    """Applies the quadratic formula to the polynomial
    ax^2 + bx + c."""
    if plus:
        return (-b + sqrt(square(b) - 4 * a * c)) / (2 * a)
    else:
        return (-b - sqrt(square(b) - 4 * a * c)) / (2 * a)

# good
def find_quadratic_root(a, b, c, plus=True):
    """Applies the quadratic formula to the polynomial
    ax^2 + bx + c."""
    disc_term = sqrt(square(b) - 4 * a * c)
    if not plus:
        disc_term *= -1
    return (-b + disc_term) / (2 * a)

# Local assignment
def percent_difference(x, y):
    difference = abs(x-y)
    return 100 * difference / x

diff = percent_difference(40, 50)
if False: # change to True to see effect
    difference # not in local frame

# The nonlocal statement
def make_withdraw(balance):
    def withdraw(amount):
        nonlocal balance
        if amount > balance:
            return 'Insufficient funds'
        balance = balance - amount
        return balance
    return withdraw

withdraw = make_withdraw(100)
withdraw(25)
withdraw(25)
withdraw(60)
withdraw(15)

# Error without nonlocal
if False: # change to True to see effect
    def make_withdraw(balance):
        def withdraw(amount):
            if amount > balance:
                return 'Insufficient funds'
            balance = balance - amount
            return balance
        return withdraw

    withdraw = make_withdraw(100)
    withdraw(25)

# Local state using mutable data type
def make_withdraw_list(balance):
    b = [balance]
    def withdraw(amount):
        if amount > b[0]:
            return 'Insufficient funds'
        b[0] = b[0] - amount
        return b[0]
    return withdraw

withdraw = make_withdraw_list(100)
withdraw(25)

# Create two withdraw functions
wd = make_withdraw(100)
wd2 = make_withdraw(100)
wd(25)
wd2(15)

# Multiple references to a withdraw function
wd = make_withdraw(100)
wd2 = wd
wd(25)
wd2(15)

# Referential transparency
wd = make_withdraw(100)
wd(25) + wd(15)
75 + 85