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List Methods

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Operations	what it does
len(dictionary)	Returns the number of items in the dictionary
for key in dictionary	Iterates over each key in the dictionary
for key, value in dictionary.items()	Iterates over each key,value pair in the dictionary
if key in dictionary	Checks whether the key is in the dictionary
dictionary[key]	Accesses the item with key key of the dictionary
dictionary[key] = value	Sets the value associated with key
del dictionary[key]	Removes the item with key key from the dictionary

Methods	what it does
dict.get(key, default)	Returns the element corresponding to key, or default if it’s not present
dict.keys()	Returns a sequence containing the keys in the dictionary
dict.values()	Returns a sequence containing the values in the dictionary
dict.update(other_dictionary)	Updates the dictionary with the items coming from the other dictionary. Existing entries will be replaced; new entries will be added.
dict.clear()	Removes all the items of the dictionary

documentation for dictionary operations and methods

Iterating Through .keys() method

Need to go through this one more time!!!

a_dict = {'color': 'blue', 'fruit': 'apple', 'pet': 'dog'}
keys = a_dict.keys()
keys
dict_keys(['color', 'fruit', 'pet'])

for key in a_dict.keys():
    print(key)
#OUTPUT
color
fruit
pet

for key in a_dict.keys():
    print(key, '->', a_dict[key])
#OUTPUT
color -> blue
fruit -> apple
pet -> dog

values() and .keys() return view objects just like .items(),

Iterating through .values() method

a_dict = {'color': 'blue', 'fruit': 'apple', 'pet': 'dog'}
values = a_dict.values()
values
dict_values(['blue', 'apple', 'dog'])

for value in a_dict.values():
    print(value)
# OUTPUT
blue
apple
dog

Store the number of files corresponding to each extension.

file_counts ={
	"jpeg":10,
	"txt":14,
	"csv":2,
	"py":23
	}
print(file_counts)
{'jpeg': 10, 'txt': 14, 'csv': 2, 'py': 23}

Find out how many text files there are in the dictionary. use the key txt to access its associated value. 

file_counts = {"jpeg": 10, "txt": 14, "csv": 2, "py": 23}
file_counts["txt"]
#OUTPUT 
14

To check if a key is contained in a dictionary using the in keyword.
It will return True if the key is found in the dictionary; otherwise it will return False.

file_counts = {"txt": 14, "csv": 2, "py": 23}
"jpeg" in file_counts
True
"html" in file_counts 
False

Dictionaries are mutable, (can be modified by adding, removing, and replacing elements in a dictionary, similar to lists).

add entry

• Dictionaries are mutable (can add remove and replace entries). 
• To add an entry in a dictionary, just use the square brackets to create the key and assign a new value to it. 

file_counts = {'txt': 14, 'csv': 2, 'py': 23, 'cfg': 8} 
file_counts["cfg"] = 8 
print(file_counts)
# OUTPUT
{'txt': 14, 'csv': 2, 'py': 23, 'cfg': 8} 

modify the value of an existing key

• keys inside of a dictionary are unique. 
• When you use a key that already exists to set a value, the value that was already paired with that key is replaced. 

file_counts["csv"] = 17
print(file_counts)
# Before
{'txt': 14, 'csv': 2, 'py': 23, 'cfg': 8}
# After
{'txt': 14, 'csv': 17, 'py': 23, 'cfg': 8}

delete entry

• delete elements from a dictionary with the del keyword by passing the dictionary and the key to the element as if we were trying to access it. 

  file_counts ={'jpeg': 10, 'txt': 14, 'csv': 17, 'py': 23, 'cfg': 8}
  del file_counts["cfg"]
  print(file_counts)
  file_counts ={'jpeg': 10, 'txt': 14, 'csv': 17, 'py': 23}
  

Iterating over the Contents of a Dictionary

file_counts ={'jpeg': 10, 'txt': 14, 'csv': 17, 'py': 23}
for key in file_counts: 
	print(key)
#OUPUT
jpg
txt
csv
py

to get access to the values

>>> for key in a_dict:
...     print(key, '->', file_counts[key])
	# indexing operator []
jpeg -> 10
txt -> 14
csv -> 17
py -> 23

Iterating Through .items() method

• returns a new view of the dictionary’s items:

a_dict = {'color': 'blue', 'fruit': 'apple', 'pet': 'dog'}
d_items = a_dict.items()
d_items  # Here d_items is a view of items
dict_items([('color', 'blue'), ('fruit', 'apple'), ('pet', 'dog')])

• d_items provides a dynamic view on the dictionary’s entries => when the dictionary changes, the views reflect these changes. alternative using the view object returned by .items():

for item in a_dict.items():
...     print(item)
...
('color', 'blue')
('fruit', 'apple')
('pet', 'dog')

for item in a_dict.items():
	print(type(item))
#OUTPUT
('color', 'blue')
<class 'tuple'>
('fruit', 'apple')
<class 'tuple'>
('pet', 'dog')
<class 'tuple'>

Now you can do tuple unpacking to iterate through the keys and values.

for key, value in a_dict.items():
...     print(key, '->', value)
...
color -> blue
fruit -> apple
pet -> dog
# now more readable and Pythonic.

values() and .keys() return view objects just like .items(),

Iterating Through .keys() method

a_dict = {'color': 'blue', 'fruit': 'apple', 'pet': 'dog'}
>>> keys = a_dict.keys()
>>> keys
dict_keys(['color', 'fruit', 'pet'])

for key in a_dict.keys():
...     print(key)
...
color
fruit
pet

for key in a_dict.keys():
...     print(key, '->', a_dict[key])
...
color -> blue
fruit -> apple
pet -> dog

Iterating Through .values() method

a_dict = {'color': 'blue', 'fruit': 'apple', 'pet': 'dog'}
values = a_dict.values()
values
dict_values(['blue', 'apple', 'dog'])

for value in a_dict.values():
...     print(value)
...
blue
apple
dog

a dictionary in a for loop, 

• the iteration variable will go through the keys in the dictionary.
• to access the associated values,
  • use the keys as indexes of the dictionary or
  • use the items method which returns a tuple for each element in the dictionary. 
    • The tuple’s first element is the key. 
    • Its second element is the value. 

file_counts ={'jpeg': 10, 'txt': 14, 'csv': 2, 'py': 23}
for ext, amount in file_counts.items(): 
  print("there are {} files with the .{} extension".format(amount, ext)) 

#OUTPUT
> there are 10 files with the .jpgextension
> there are 14 files with the .txtextension
> there are 2 files with the .csvextension
> there are 23 files with the .pyextension

To access the keys of a dictionary or the values with their corresponding dictionary methods  

print(file_counts.keys())
dict_keys(['jpg', 'txt', 'csv', 'py'])

print(file_counts.values())
dict_values([10, 14, 2, 23])

These methods return special data types related to the dictionary. => just iterate them as you would with any sequence.

for value in file_counts.values(): 
   print(value)
10
14
2
23

• use items to get key value pairs, file_counts.items()
• keys to get the keys, and file_counts.keys()
• values to get the values. file_counts.values()

Formatting

• single for the dict and double for formatting.

>>> comedian = {'name': 'Eric Idle', 'age': 74}
>>> f"The comedian is {comedian['name']}, aged {comedian['age']}."
The comedian is Eric Idle, aged 74.

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