Python Learning notes-dictionaries (bottom)

as with lists and strings, dictionaries also have methods.

1. Clear clears all items in the dictionary.

We can assign an empty dictionary to a dictionary to empty its entries. You can also completely empty the dictionary using the Clear method.

x= {}y=xx[' age ']= ' + ' x[' gender ']= ' Male ' Print x x.clear () print x print y {' gender ': ' Male ', ' age ': ' 25 '}{}{}

If you change X.clear to x={}, the result becomes

{' Gender ': ' Male ', ' age ': ' 25 '} {} {' gender ': ' Male ', ' age ': ' 25 '}

2. Shallow copy and deep copy

The former refers to a value of modify copy's dictionary, which in the original dictionary also changes, and vice versa.

x= {}x[' age ']=[' + ', ' + ', ' []] #Listx [' Gender ']= ' Male ' #Stringy =x.copy () x[' age '].remove (' + ') y[' age '].remove (' 26 ') Print x print y {' gender ': ' Male ', ' age ': [']}{' gender ': ' Male ', ' age ': [' 28 ']}

If you use deep copy deepcopy, the original dictionary and the copy dictionary are completely independent

From copy import deepcopyx= {}x[' age ']=[', ' + ', ' + '] #Listx [' Gender ']= ' Male ' #Stringy =deepcopy (x) x[' age '].append ( ' + ') y[' age '].remove (' + ') print x print y {' gender ': ' Male ', ' age ': [' + ', ' + ', ' + ', ' + ']}{' gender ': ' Male ', ' age ': [' 2 5 ', ' 28 ']}

3. Fromkeys creates a dictionary with the given keys, the default value is None

What errors do you see here?

x= {}.fromkeys (' name ', ' gender ') print x {' A ': ' Gender ', ' e ': ' Gender ', ' m ': ' Gender ', ' N ': ' Gender '}

The correct form for

x= {}.fromkeys ([' Name ', ' gender ']) print x {' Gender ': none, ' Name ': none}

4. Get can access items that do not exist in a dictionary

x= {}print x.get (' age ') None

More flexibility in responding to items that are not in the user input dictionary

A few simple ways:

5. Has_key is used to check if a dictionary has a specified key, and it can be implemented in.

6. Pop is used to get the value of the given key and delete the item from the dictionary.

info = {' Alice ': {' phone ': ' 2342 ', ' addr ': ' Taierzhuang Rd '}, ' Bob ': { ' Phone ': ' 2242 ', ' addr ': ' Jinqiao Rd '}}info.pop (' Alice ') print info{' Bob ': {' phone ': ' 2242 ', ' Ad Dr ': ' Jinqiao Rd '}}

7.setdefault is used to add a key (you can add a key if the key does not exist, unlike get, it will change the original dictionary)

8.items & Iteritems

Items returned as a list of items in the dictionary, Iteritems returns an iterator

info = {         ' Alice ': {                  ' phone ': ' 2342 ',                  ' addr ': ' Taierzhuang rd '},          ' Bob ':{                 ' phone ': ' 2242 ',                  ' addr ': ' Jinqiao rd '}         }print infoprint info.items () Print info.iteritems () {' Bob ':  {' phone ':  ' 2242 ',   ' addr ':  ' jinqiao rd '},  ' Alice ':  {' phone ':  ' 2342 ',  ' ' addr ':  ' Taierzhuang rd '}}[(' Bob ',  {' phone ':  ' 2242 ',  ' addr ':  ' jinqiao rd '}),  (' Alice ',  {' phone ':  ' 2342 ',  ' addr ':  ' Taierzhuang rd '})]<dictionary-itemiterator object at 0x10a200a48> 

The same, keys and Iterkeys return keys, values, and itervalues return value.

9.update update the other with one dictionary item.

d={' title ': ' Python Web site ', ' url ': ' http://www.python.org ', ' changed ': ' April 4 20:18 '}x={' title ': ' Pyth On Language Website '}print d.update (x)

Note that at this point the output is none, do not know why, put the last step above to write separately:

D.update (x) print d{' url ': ' http://www.python.org ', ' changed ': ' April 4 20:18 ', ' title ': ' Python Language Website '}

Python Learning notes-dictionaries (bottom)