In which dad explains how arrays are used to look up modular results

dad_stop_showing_off.py

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+'''Flamingo, by the immortal Herb Jeffries'''
+
+year = int(raw_input("What year were you born? "))
+
+if year == 1971:
+  print "You must be pretty cool to have been born in " + str(year) + "."
+else:
+  print "Well we can't all be cool I suppose."
+
+print "You are about " + str(2017 - year) + " years old."
+
+# Here are four random animals
+oreilly_cover_animals = ["aardvark", "bonobo", "camel", "dik-dik"]
+
+'''random.randint(0,3) will always be 0, 1, 2, or 3
+
+As a result, the index value used in oreilly_cover_animals
+will never be "out of bounds" (less than 0 or greater than 3)'''
+import random
+print "Your spirit animal is a " + oreilly_cover_animals[random.randint(0,3)]
+
+""" Same trick for any cyclical data structure
+
+By taking % N you always guarantee a number between 0 and N"""
+chinese_year_animals = [
+  "rat", "ox", "tiger", "rabbit", "dragon", "snake",
+  "horse", "goat", "monkey", "rooster", "dog", "pig"
+]
+
+'''
+Note that 1912 is an arbitary choice for zodiac_start_year. I could have
+chosen any Year of the Rat.  Why? Because all I want is a year such
+that year - zodiac_start_year is:
+
+(N*12 + 0) for anyone born in the Year of the Rat
+(N*12 + 1) for anyone born in the Year of the Ox
+(N*12 + 2) for anyone born in the Year of the Tiger
+...
+etc.
+
+So imagine your birth year is 1948. By the math I'm using then
+
+1948 - zodiac_start_year = 1948 - 1912 = 36
+but 36 = 3*12 + 0, and (3*12 + 0) % 0 = 0 ==> chinese_year_animals[0] => 'rat'
+
+But I also could have chosen my zodiac_start_year to be 1900. Then
+
+1948 - zodiac_start_year = 1948 - 1900 = 48
+but 48 = 4*12 + 0, and (4*12 + 0) % 0 = 0 ==> chinese_year_animals[0] => 'rat'
+
+I even could have chosen my zodiac_start_year to be 1960!
+
+1960 - zodiac_start_year = 1948 - 1960 = -12
+but -12 = -1*12 + 0, and (-1*12 + 0) % 0 = 0 ==> chinese_year_animals[0] => 'rat'
+
+So the choice of zodiac_start_year doesn't matter as long as it's a year that
+corresponds with the zeroth element in the chinese_year_animals array. It even
+works when the zodiac_start_year is later than the input year, because we're
+just going around in circles of length 12 years, backwards or forwards, it
+doesn't matter.
+
+Extra credit for smarty-pants: I could also put "ox" as the zeroth element
+in the chinese_year_animals array and use 1913 or 1925 or 1937 as my "year 0".
+
+If I did that, where would "rat" go in the chinese_year_animals array?
+Think about it!
+'''
+zodiac_start_year = 1912
+your_animal = chinese_year_animals[(year - zodiac_start_year) % 12]
+print "But unfortunately your Chinese zodiac animal is just a lame old " + your_animal + "."