15-112 Fundamentals of Programming

# single-quoted or double-quoted strings are the most common
print('single-quotes')
print("double-quotes")

# triple-qouted strings are less common (though see next section for a typical use)
print('''triple single-quotes''')
print("""triple double-quotes""")

print("abc\ndef")  # \n is a single newline character
print("""abc
def""")

print("""\
You can use a backslash at the end of a line in a string to exclude
the newline after it. This should almost never be used, but one good
use of it is in this example, at the start of a multi-line string, so
the whole string can be entered with the same indentation (none, that is).
""")

print("Double-quote: \"")
print("Backslash: \\")
print("Newline (in brackets): [\n]")
print("Tab (in brackets): [\t]")

print("These items are tab-delimited, 3-per-line:")
print("abc\tdef\tg\nhi\tj\\\tk\n---")

s = "a\\b\"c\td"
print("s =", s)
print("len(s) =", len(s))

s = "abc" "def"  # ok (but "abc" + "def" is preferred)
print(s)
s = s "def" # error (only works with string literals, not variables)

"""
Python does not have multiline comments, but you can do something similar
by using a top-level multiline string, such as this. Technically, this is
not a comment, and Python will evaluate this string, but then ignore it
and garbage collect it!
"""
print("wow!")

import string
print(string.ascii_letters)   # abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
print(string.ascii_lowercase) # abcdefghijklmnopqrstuvwxyz
print("-----------")
print(string.ascii_uppercase) # ABCDEFGHIJKLMNOPQRSTUVWXYZ
print(string.digits)          # 0123456789
print("-----------")
print(string.punctuation)     # '!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~'
print(string.printable)       # digits + letters + punctuation + whitespace
print("-----------")
print(string.whitespace)      # space + tab + linefeed + return + ...

names = "fred,wilma,betty,barney"
for name in names.split(","):
    print(name)

# quotes from brainyquote.com
quotes = """\
Dijkstra: Simplicity is prerequisite for reliability.
Knuth: If you optimize everything, you will always be unhappy.
Dijkstra: Perfecting oneself is as much unlearning as it is learning.
Knuth: Beware of bugs in the above code; I have only proved it correct, not tried it.
Dijkstra: Computer science is no more about computers than astronomy is about telescopes.
"""
for line in quotes.splitlines():
    if (line.startswith("Knuth")):
        print(line)

# Run this code to see a table of isX() behaviors
def p(test):
    print("True     " if test else "False    ", end="")
def printRow(s):
    print(" " + s + "  ", end="")
    p(s.isalnum())
    p(s.isalpha())
    p(s.isdigit())
    p(s.islower())
    p(s.isspace())
    p(s.isupper())
    print()
def printTable():
    print("  s   isalnum  isalpha  isdigit  islower  isspace  isupper")
    for s in "ABCD,ABcd,abcd,ab12,1234,    ,AB?!".split(","):
        printRow(s)
printTable()

print("This is nice. Yes!".lower())
print("So is this? Sure!!".upper())
print("   Strip removes leading and trailing whitespace only    ".strip())
print("This is nice.  Really nice.".replace("nice", "sweet"))
print("This is nice.  Really nice.".replace("nice", "sweet", 1)) # count = 1

print("----------------")
s = "This is so so fun!"
t = s.replace("so ", "")
print(t)
print(s) # note that s is unmodified (strings are immutable!)

print("This is a history test".count("is")) # 3
print("This IS a history test".count("is")) # 2
print("-------")
print("Dogs and cats!".startswith("Do"))    # True
print("Dogs and cats!".startswith("Don't")) # False
print("-------")
print("Dogs and cats!".endswith("!"))       # True
print("Dogs and cats!".endswith("rats!"))   # False
print("-------")
print("Dogs and cats!".find("and"))         # 5
print("Dogs and cats!".find("or"))          # -1
print("-------")
print("Dogs and cats!".index("and"))        # 5
print("Dogs and cats!".index("or"))         # crash!

breed = "beagle"
print("Did you see a %s?" % breed)

dogs = 42
print("There are %d dogs." % dogs)

grade = 87.385
print("Your current grade is %f!" % grade)

grade = 87.385
print("Your current grade is %0.1f!" % grade)

dogs = 42
cats = 18
exclamation = "Wow"
print("There are %d dogs and %d cats. %s!!!" % (dogs, cats, exclamation))

dogs = 42
cats = 3
print("%10s %10s" % ("dogs", "cats"))
print("%10d %10d" % (dogs, cats))

dogs = 42
cats = 3
print("%-10s %-10s" % ("dogs", "cats"))
print("%-10d %-10d" % (dogs, cats))

def readFile(path):
    with open(path, "rt") as f:
        return f.read()

def writeFile(path, contents):
    with open(path, "wt") as f:
        f.write(contents)

contentsToWrite = "This is a test!\nIt is only a test!"
writeFile("foo.txt", contentsToWrite)

contentsRead = readFile("foo.txt")
assert(contentsRead == contentsToWrite)

print("Open the file foo.txt and verify its contents.")

def encrypt(message, shiftNum):
    result = ""
    for char in message:
        result += shift(char, shiftNum)
    return result
 
def shift(char, shiftNum):
    shiftNum = shiftNum % 26
    if(not char.isalpha()): return char
    shiftedOrd = ord(char) + shiftNum
    if char.islower():
        distanceFromOrigin = (shiftedOrd - ord('a')) % 26
        return chr(ord('a') + distanceFromOrigin)
    else:
        distanceFromOrigin = (shiftedOrd - ord('A')) % 26
        return chr(ord('A') + distanceFromOrigin)

# An alternative solution
def shift(char, shiftNum):
    shiftNum = shiftNum % 26
    if(not char.isalpha()): return char
    shifted = ord(char) + shiftNum
    if ( ((char <= 'Z') and (shifted > ord('Z'))) or
         ((char <= 'z') and (shifted > ord('z')))):
        return chr(shifted - 26)
    else:
        return chr(shifted)