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Global and local Variables

count = 0

def countUp():
	count += 1
	return count

print(countUp)
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Dictionary is like a list but with named indices called keys

The dictionary is map between keys and values
Every item is a key-value pair

"one" => "uno"
"two" => "dos"
"three" = > "tres"

>>> eng2sp = {"one":"uno", "two":"dos", "three":"tres"}
>>> print(eng2sp)
>>> {'three': 'tres', 'two': 'dos', 'one': 'uno'}
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We can check if a key exists in the dictionary by using the in operator

if 'one' in eng2sp:
	print("true")
	
if 'uno' in eng2sp:
	print("true")
	
if 'uno' not in eng2sp:
	print("true")


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dict.values() returns a list of all the values in the dictionary

values = eng2sp.values()
print(values)
["uno", "dos", "tres"]

if 'uno' in values:
	print("true")
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Counting the occurence of letters in a string

def histogram(string):
	# countLetters takes 1 argument, any string
	# it returns a dictionary with the frequency of each letter in the string
	
	# create an empty dictionart
	d = dict()
	# iterate through each character in the string
	for char in string:
		# if it is the first time we see the character, set its count to 1
		if char not in d:
			d[char] = 1
		# if the count for character is already in the dictionary, add 1 to it
		else:
			d[char] += 1
	# return the resulting dictionary so we can save it and use it later
	return d
	
	
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# Print the histogram
def print_histogram(h):
	# Iterate thrugh each key, and print the key and the value
	for key in h:
		print(key, h[key])
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Opening a file in your directory

file_handle = open("filename", mode)

Store the entire file in a string
whole_thing = file_handle.read()

Storing it as a list of lines
lines = file_handle.readlines()

file_handle.close()
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Modes
"r"		Read from a file, crash if it does not exits
"w"		Write to a file, create it if it does not exist and overwrite it if it already exists
"a"		Append to a file, start at the end, if a file does not exist create it
"r+"	Read and Write to a file, crash if it does not exist
"w+"	Write and Read from a file, create it if it does not exist and overwrite it if it already exists
"a+"	Append and Read from a file, start at end and create it if it does not exits
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Exercise
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