Basic python tutorials-A Dictionary of notes

Basic python tutorials-A Dictionary of notes

• Create dictionary

A dictionary consists of multiple key-value pairs. Each key and corresponding value are separated by a colon, and items are separated by a comma. The entire dictionary is enclosed by a pair of braces, as shown in figure

>>> Phonebook = {'Alice ': '000000', 'betch': '000000', 'cecil': '000000 '}
>>> Phonebook
{'Betch': '000000', 'Alice ': '000000', 'cecil': '000000 '}

Dict-create a dictionary through a sequence pair or keyword such as other ing, (Key, value), such

>>> Items = [('name', 'gtum '), ('age', 42)]
>>> D = dict (items)
>>> D
{'Age': 42, 'name': 'gtum '}
>>> D ['age']
42
>>> D = dict (name = 'gtum ', age = 42)
>>> D
{'Age': 42, 'name': 'gtum '}

• Basic operations

Len (d) -- returns the number of keys (key-value pairs) in d.

D [k] -- returns the value associated with the key k.

D [k] = v -- associate value v with key k

Del d [k] -- delete an item whose key is k

K in d -- check whether d contains k-key items.

The differences between dictionaries and lists are as follows:

Key type: the dictionary key can be any unchangeable type.

Auto-add: that is, the key does not exist in the dictionary at first, or you can assign a value to it.

>>> X = {}
>>> X [42] = 'F'
>>> X
{42: 'F '}

Membership: k in d searches for keys

# Simple database # use the name of a person as the key dictionary. Each person uses another dictionary to indicate their phone numbers and addresses, respectively. The keys 'phone' and 'add' indicate their phone numbers and addresses, people = {'Alice ': {'phone': '123 ', 'addr ': 'foo drive 23'}, 'bes': {'phone': '000000', 'addr': 'bar Street 42'}, 'cecil ': {'phone': '000000', 'add': 'baz avenue 90' }}# descriptive tags used for phone numbers and addresses, labels = {'phone': 'phone number', 'add': 'address'} name = raw_input ('name: ') will be used to print the output :') # Find the phone number or address? Use the correct key: request = raw_input ('key (p/a): ') # use the correct key: if request = 'P ': key = 'phone' if request = 'A': ker = 'add' # if the name is a valid key in the dictionary, the information is printed if name in people: print "% s's % s is % s. "% \ (name, labels [key], people [name] [key])

Result

Name: Beth
Key (p/a): p
Beth's phone number is 9102.

• Dictionary Format String

Only use a string as the key dictionary to format the string, as shown in figure

>>> Phonebook = {'Alice ': '000000', 'betch': '000000', 'cecil': '000000 '}
>>> "Alice's phnoe is % (alice) s." % phonebook
"Alice's phnoe is 0123 ."

• Dictionary Method

Clear -- clear all the items in the dictionary and directly apply to the original dictionary

Copy -- returns a salary point with the same key-value pair.

>>> X = {'username': 'admin', 'machines ': ['foo', 'bar']}
>>> Y = x. copy ()
>>> Y ['username'] = 'mlh'
>>> Y ['machines ']. remove ('foo ')
>>> Y
{'Username': 'mlh', 'machines ': ['bar']}
>>> X
{'Username': 'admin', 'machines ': ['bar']}

Deecopy -- deep copy

Fromkeys -- use the given key to create a new dictionary. The default value of each key is None, or you can provide the default value.

>>> X = dict. fromkeys (['name', 'age'], 'UN ')
>>> X
{'Age': 'non', 'name': 'non '}

Get -- access dictionary. If you access a key that does not exist, None is returned or the default value is customized.

>>> X. get ('it', 'n'/')
'N'/'

# Use the get () simple database people = {'Alice ': {'phone': '000000', 'addr ': 'foo drive 23'}, 'beth ': {'phone ': '123456', 'addr': 'bar Street 42'}, 'cecil ': {'phone': '123456', 'addr ': 'baz avenue 90' }}# use labels = {'phone': 'phone number' when printing and outputting descriptive labels for phone numbers and addresses ', 'addr ': 'address'} name = raw_input ('name:') # Find the phone number or address? Request = raw_input ('key (p/a): ') # use the correct key: key = request # if the request is neither 'P' nor 'A' if request = 'P': key = 'phone' if request = 'A ': key = 'add' # Use get () to provide the default value "person = people. get (name, {}) label = labels. get (key, key) result = person. get (key, 'not available') print "% s is % s. "% \ (name, label, result)

The result is as follows:

Name: Beth
Key (p/a):
Beth's address is Bar Street 42.

Has_key -- check whether the dictionary contains the given key

Items -- returns all dictionary items in the list. Each item in the list comes from (Key, value)

Iteritems -- Return iterator

Keys -- returns the keys in the dictionary as a list

Iterkeys -- return the iterator for the key

Pop -- obtain the value corresponding to the given key, and then remove the key-value pair from the dictionary.

Popitem -- a random item is displayed.

Setdefault -- get the value associated with the given key, and set the corresponding key value if the dictionary does not contain the given key

>>> X = {'username': 'admin', 'machines ': ['foo', 'bar']}
>>> X. pop ('username ')
'Admin'
>>> X = {'username': 'admin', 'machines ': ['foo', 'bar']}
>>> X. setdefault ('hh ', 'n'/')
'N'/'
>>> X
{'Username': 'admin', 'hh': 'n'/A', 'machines ': ['foo', 'bar']}
>>> X ['hh'] = 'hh'
>>> X. setdefault ('hh ', 'n'/')
'Hh'
>>> X
{'Username': 'admin', 'hh': 'hh', 'machines ': ['foo', 'bar']}

Update -- use one dictionary item to update another dictionary item. The provided dictionary items will be added to the old dictionary. If the same key exists, it will be overwritten.

>>> X = {'username': 'admin', 'machines ': ['foo', 'bar']}
>>> Y = {'hh ': 'hahaha '}
>>> X. update (y)
>>> X
{'Username': 'admin', 'hh': 'hahaha', 'machines ': ['foo', 'bar']}

Values -- returns the value in the dictionary in the form of a list. The list can contain duplicate elements.