15-112 Fundamentals of Programming

def countToN(n):
    counter = 1       
    while(True):
        print(counter)
        if(counter == n):
            break
        counter += 1
    print("bye!")

def sumOfOddsToN(n):
    total = 0
    for x in range(1, n+1):
        if(x % 2 == 0):
            continue
        total += x
    return total

# Below y is an optional parameter.
# When calling the function, if a second argument is given, that value
# will be assigned to y. If a second argument is not given, by default,
# y will be assigned the value 10.  
def f(x, y=10): 
    return x+y

print(f(5))   # prints 15
print(f(5,6)) # prints 11

print(math.factorial(20))  # we did not first import the math module

# Python output:
#   NameError: name 'math' is not defined

print(math.factorial(20))  # we did not first import the math module

# Python output:
#   NameError: name 'math' is not defined

# list all the functions in the math module
# (ignore items in __double_underscores__)
import math
print(dir(math))

# even better, read the online docs!
import webbrowser
input("Hit enter to see the online docs for the math module.")
webbrowser.open("https://docs.python.org/3/library/math.html")

print(0.1 + 0.1 == 0.2)        # True, but...
print(0.1 + 0.1 + 0.1 == 0.3)  # False!
print(0.1 + 0.1 + 0.1)         # prints 0.30000000000000004 (uh oh)
print((0.1 + 0.1 + 0.1) - 0.3) # prints 5.55111512313e-17 (tiny, but non-zero!)

print("The problem....")
d1 = 0.1 + 0.1 + 0.1
d2 = 0.3
print(d1 == d2)                # False (never use == with floats!)

print()
print("The solution...")
epsilon = 10**-10
print(abs(d2 - d1) < epsilon)  # True!

print()
print("Once again, using a useful helper function, almostEqual:")

def almostEqual(d1, d2):
    epsilon = 10**-10
    return (abs(d2 - d1) < epsilon)

d1 = 0.1 + 0.1 + 0.1
d2 = 0.3
print(d1 == d2)            # still False, of course
print(almostEqual(d1, d2)) # True, and now packaged in a handy reusable function!

def yes():
    return True

def no():
    return False

def crash():
    return 1/0 # crashes!

print(no() and crash()) # Works!
print(crash() and no()) # Crashes!
print (yes() and crash()) # Never runs (due to crash), but would also crash (without short-circuiting)

def yes():
    return True

def no():
    return False

def crash():
    return 1/0 # crashes!

print(yes() or crash()) # Works!
print(crash() or yes()) # Crashes!
print(no() or crash())  # Never runs (due to crash), but would also crash (without short-circuiting)

def isPositive(n):
    result = (n > 0)
    print("isPositive(",n,") =", result)
    return result

def isEven(n):
    result = (n % 2 == 0)
    print("isEven(",n,") =", result)
    return result

print("Test 1: isEven(-4) and isPositive(-4))")
print(isEven(-4) and isPositive(-4)) # Calls both functions
print("----------")
print("Test 2: isEven(-3) and isPositive(-3)")
print(isEven(-3) and isPositive(-3)) # Calls only one function!

# if-else expression (not an if-else statement!)

def abs7(n):
    return n if (n >= 0) else -n

print("abs7(5) =", abs7(5), "and abs7(-5) =", abs7(-5))

print("abc" + "def")
print("abc" * 3)
print("abc" + 3)  # error

print("ring" in "strings")
print("wow" in "amazing!")
print("Yes" in "yes!")
print("" in "No way!")

s = "abcdefgh"
print(s)
print(s[0])
print(s[1])
print(s[2])

print("-----------")
print(s[len(s)-1])
print(s[len(s)])  # crashes (string index out of range)

s = "abcdefgh"
print(s)
print(s[-1])
print(s[-2])

s = "abcdefgh"
print(s)
print(s[0:3])
print(s[1:3])
print("-----------")
print(s[2:3])
print(s[3:3])

s = "abcdefgh"
print(s)
print(s[3:])
print(s[:3])
print(s[:])

print("This is not as common, but perfectly ok.")
s = "abcdefgh"
print(s)
print(s[1:7:2])
print(s[1:7:3])

s = "abcdefgh"

print("This works, but is confusing:")
print(s[::-1])

print("This also works, but is still confusing:")
print("".join(reversed(s)))

print("Best way: write your own reverseString() function:")

def reverseString(s):
    return s[::-1]

print(reverseString(s)) # crystal clear!

s = "abcd"
for i in range(len(s)):
    print(i, s[i])

s = "abcd"
for c in s:
    print(c)

s = "abcde"
s[2] = "z"  # Error! Cannot assign into s[i]

s = "abcde"
s = s[:2] + "z" + s[3:]
print(s)

name = input("Enter your name: ")
print("Hi, " + name + ". Your name has " + str(len(name)) + " letters!")

print(ord("A")) # 65
print(chr(65))  # "A"
print(chr(ord("A")+1)) # ?

# eval() works but you should not use it!
s = "(3**2 + 4**2)**0.5"
print(eval(s))

# why not? Well...
s = "reformatMyHardDrive()"
print(eval(s)) # no such function!  But what if there was?

def convertToLowercase(character):
  distance = ord("a") - ord("A")
  return chr(ord(character) + distance)

# There are many ways to write isPalindrome(s)
# Here are several.  Which way is best?

def reverseString(s):
    return s[::-1]

def isPalindrome1(s):
    return (s == reverseString(s))

def isPalindrome2(s):
    for i in range(len(s)):
        if (s[i] != s[len(s)-1-i]):
            return False
    return True

def isPalindrome3(s):
    for i in range(len(s)):
        if (s[i] != s[-1-i]):
            return False
    return True

def isPalindrome4(s):
    while (len(s) > 1):
        if (s[0] != s[-1]):
            return False
        s = s[1:-1]
    return True

print(isPalindrome1("abcba"), isPalindrome1("abca"))
print(isPalindrome2("abcba"), isPalindrome2("abca"))
print(isPalindrome3("abcba"), isPalindrome3("abca"))
print(isPalindrome4("abcba"), isPalindrome4("abca"))