'''
##### Lecture 6 #####
# Michelle Szucs

# To download as a Python file, right-click the link
# and select "Save link as..."

print "Basic dictionary examples"

# Creating a dictionary
passingDict = {'student1': True, 'student2': False}
print "passingDict example 1:", passingDict
# We can also add more values
passingDict['student3'] = True



# You can also put items in the dictionary after you
# declare it
# Making an empty dictionary
passingDict = {}
# Adding items to the dictionary
passingDict['student1'] = True
passingDict['student2'] = False
print "passingDict example 3:", passingDict
# Keys can only be associated with one value -
# the following line of code changes the value
# of 'student2' (it doesn't add a second value)
passingDict['student2'] = True
print "passingDict example 4:", passingDict

# Here's how you can access a specific value
print "Accessing a value: passingDict['student2'] is", passingDict['student2']

# Trying to access a key that isn't in the
# dictionary will result in a KeyError
# Uncomment the following line of code to see
# the code throw an error
#print passingDict['student3']


print # This prints an empty line to separate the code
print "Frequency dictionary examples"
'''

# As a frequency dictionary
# Insert print statements into this function to follow
# its flow if you find it confusing
def makeFreqDictOne(word):
    frequency = {}
    for letter in word:
        # need to check whether the key exists to
        # avoid a KeyError
        # if letter is already a key
        if letter in frequency: # checks if letter is a key
            # if it is, increase count by 1
            frequency[letter] += 1
        # if I haven't added the letter yet
        else:
            # add it, make the count 1
            frequency[letter] = 1
        # This if-else block prevents code from try to access
        # the value of a key that doesn't exist.
    return frequency
frequencyDict = makeFreqDictOne("Mississippi")
print "Original frequency dictionary #1:", frequencyDict
'''

# Here's another way of making the frequency dictionary
# the "get" method takes two arguments: the key whose value
# you want to access, and a value to be returned if a key
# error is thrown.
# If the key is in the dictionary, its value will be returned.
# If the key is not in the dictionary, the second argument
# that "get" takes will be returned.
# In this case, if the key is in the dictionary, the integer
# value it's associated with is returned (the count of that
# letter so far).
# If the key isn't in the dictionary, 0 is returned.
# I then reassign the value associated with the key to the
# value produced by get plus one - I'm just incrememnting
# the count for that letter.
def makeFreqDictTwo(word):
    frequency = {}
    for letter in word:
        frequency[letter] = frequency.get(letter, 0) + 1
    return frequency

frequencyDict = makeFreqDictTwo("Mississippi")
print "Original frequency dictionary #2:", frequencyDict

print
print "Dictionary functions and tools"

# You can delete items from dictionaries using the
# del keyword
del frequencyDict['i']

print "Removed i:", frequencyDict

# The length of a dictionary is the number of
# key-value pairs
print "Length:", len(frequencyDict)

# Some dictionary functions include getting the
# keys and getting the values, both returned
# as lists
print "Keys:",frequencyDict.keys()
print "Values:",frequencyDict.values()

print
print "Dictionaries are mutable, which can cause aliasing problems"
'''
# Dictionaries are mutable, which means that they
# can be aliased - be careful when changing dictionaries
# that have different names but are actually the same
# object
alias = frequencyDict
# The following line is the correct way to copy a dictionary
copy = frequencyDict.copy()
print "Frequency dictionary:", frequencyDict
print "Alias:", alias
print "Copy:", copy
print "alias['i'] = 3"
alias['i'] = 3
print "Frequency dictionary:", frequencyDict
print "Alias:", alias
print "Copy:", copy


print
print "Checking multiple elements of a list for truth"
'''
# Checking if all items in a list satisfy a certain condition
myList = [True, False, True, True]
print "List:", myList
print "Any:", any(myList) # "or" of the list
print "All:", all(myList) # "and" of the list

# Using loops and conditionals
# I want to return true if every value in the list
# is less than 5
def lessThanFive(aList):
    # You usually need to set a boolean variable to a
    # initial condition.
    isLess = True
    for num in aList:
        # print statement so we can understand how the
        # break statement works later on - uncomment
        # if you're confused
        #print "num =", num
        if num >= 5:
            isLess = False
            # This break statment makes the for loop
            # stop once I reach a variable that's not
            # less than 5. I know I want to return False,
            # so I might as well save some time and exit early.
            break
    return isLess

## THIS IS THE WRONG WAY TO DO IT
def lessThanFiveButWrong(aList):
    isLess = True
    for num in aList:
        if num >= 5:
            return False
        else:
            return True
## This function will ONLY check the first item in the list

## THIS IS ALSO WRONG
def lessThanFiveButStillWrong(aList):
    isLess = True
    for num in aList:
        if num >= 5:
            isLess = False
        else:
            isLess = True
    return isLess
## This function will ONLY be affected by the last item

# Test cases
print
print "######### Less than 5 tests ##########"
print "Good implementation"
print "[1,2,3,4,5,6] (should be False):", lessThanFive([1,2,3,4,5,6])
print "[6,2,3,4,5,1] (should be False):", lessThanFive([6,2,3,4,5,1])
print "[1,2,3,4,-1,3] (should be True):", lessThanFive([1,2,3,4,-1,3])
print "Bad implementation 1"
print "[1,2,3,4,5,6] (should be False):", lessThanFiveButWrong([1,2,3,4,5,6])
print "[6,2,3,4,5,1] (should be False):", lessThanFiveButWrong([6,2,3,4,5,1])
print "[1,2,3,4,-1,3] (should be True):", lessThanFiveButWrong([1,2,3,4,-1,3])
print "Bad implementation 2"
print "[1,2,3,4,5,6] (should be False):", lessThanFiveButStillWrong([1,2,3,4,5,6])
print "[6,2,3,4,5,1] (should be False):", lessThanFiveButStillWrong([6,2,3,4,5,1])
print "[1,2,3,4,-1,3] (should be True):", lessThanFiveButStillWrong([1,2,3,4,-1,3])


'''