Python Learning 3-index

Dictionary: All can be called by easy to find a specific word (key), so as to find his definition (value).

To create and use a dictionary:

>>> phonebook = {' Zhang ': ' 231 ', ' Wang ': ' 123 '}

　　dict function : A dictionary can be established through the DICT function, through other mappings (such as other dictionaries) or by a sequence of (key, value) pairs

>>> Items  = [(' Name ', ' Zhang '), (' Age ', 2)]>>> d  = dict (items) >>> d{' Age ': 2, ' name ': ' Zhang '}>>> d[' name '] ' Zhang ' #dict function can also be created by keyword arguments to dictionary >>> d = dict (name = "Zhang ", age=2) >>> d{' age ': 2, ' name ': ' Zhang '}      

　　Basic operation of the dictionary

The basic behavior of a dictionary is similar to a sequence in many ways

Len (d)--Returns the number of key-value pairs in D

D[K]--Returns the value of the key K

D[k] = v--assigns the V value to the K key (if K is not in D, it is automatically added to D, different from the sequence)

Del D[k]--delete the value of the key K

K in D--check if D contains an entry with key K (Note: The key is found)

　　formatting strings for Dictionaries

Add a key after the% of each conversion specifier (in parentheses), followed by the other explanatory elements

>>> phonebook = {' Zhang ': ' 123 ', ' Wang ': ' 555 '}>>> "Zhang ' s phone number is% (Zhang) s."  Phonebook "Zhang ' s phone number is 123." 

The method of the dictionary

1.clear-Clears all items in the dictionary. No return value, or can be understood to return none

>>> d = {}>>> d[' name '] = ' Zhang ' >>> d[' age ' = 23>>> d{' age ': +, ' name ': ' ZH Ang '}>>> return_value = d.clear () >>> print return_value   

2.copy and Deepcopy replication

3.from_keys--Create a new dictionary using the key to the point

4.get more relaxed access to the dictionary method if the key does not exist returns none

5.has_key is the same as in method

6.items and Iteritems--keys and Iterkeys

Items--Returns the dictionary all items in a list, each item in the list is represented as a (key, value) pair, but not in any order

Iteritems-The function is approximately the same, but returns an iterator instead of a list

>>> d = {' Titile ': ' I am a tiger ', ' age ': Ten}>>> d.items (' age ', ten), (' Titile ', ' I am a tiger ' 
     
      )]>>> it =
       d.iteritems () >>> It<dictionary-itemiterator object at 0x02b136c0> 
     

7.pop--Used to get the value corresponding to the key and remove the pair of key values

>>> d{' age ': ten, ' titile ': ' I am a tiger '}>>> d.pop (' age ') 10>>> d{' titile ': ' I am a tiger '}
#不存在键, error >>> d.pop (' name ') Traceback (most recent): File "<pyshell#7>", line 1, in <module& Gt d.pop (' name ') keyerror: ' Name '  

8.popitem Pop-up random entries and delete

>>> d{' age ': ten, ' titile ': ' I am a tiger '}>>> d.popitem (' age ', ten) >>> d{' titile ': ' I am a Tiger '}    

9.setdefault-Similar to the Get method, the ability to get the value associated with a given key, and to set the corresponding key value without a given key in the dictionary

>>> d = {}>>> d.setdefault (' name ', ' N/a ') ' N/a ' >>> d{' name ': ' N/a '}>> > d[' name '] = ' Zhang ' >>> d.setdefault (' name ', ' N/a ') ' Zhang ' >>> d{' name ': ' Zhang '} 

10.update--Update another dictionary with one dictionary, the updated dictionary will be added to the original dictionary, the same key will be overwritten

>>> d = {' title ': ' Zhang ', ' Age ': 10}
>>> x = {' Age ': 20}
>>> d.update (x)
>>> D
{' Age ': ' title ': ' Zhang '}
>>> y = {' sex ': ' Male '}
>>> d.update (y)
>>> D
{' Age ': ' Sex ': ' Male ', ' title ': ' Zhang '}

Python Learning 3-index