A collection of practical techniques for creating, traversing, and adding dictionaries in python

The field is Python is the only key-value type in the dictionary, and is a very important data structure in Python, because it stores data in a hashed manner, with an O (1) complexity, which is very fast. The common uses of dictionaries are listed below.
List of common methods in a dictionary

The code is as follows:

#方法 #描述
-------------------------------------------------------------------------------------------------
D.clear () #移除D中的所有项
D.copy () #返回D的副本
D.fromkeys (Seq[,val]) #返回从seq中获得的键和被设置为val的值的字典. Can do class method calls
D.get (Key[,default]) #如果D [key] exists, returns it, otherwise returns the given default value of None
D.has_key (Key) #检查D是否有给定键key
D.items () #返回表示D项的 (key, value) pair list
D.iteritems () #从D. Items () Returns an iterative object in the (key, value) pair
D.iterkeys () #从D的键中返回一个可迭代对象
D.itervalues () #从D的值中返回一个可迭代对象
D.keys () #返回D键的列表
D.pop (Key[,d]) #移除并且返回对应给定键key或给定的默认值D的值
D.popitem () #从D中移除任意一项 and returns it as a (key, value) pair
D.setdefault (Key[,default]) #如果D [key] exists and returns it, otherwise the default value of None is returned.
D.update (Other) #将other中的每一项加入到D中.
D.values () #返回D中值的列表

Ii. Five ways to create a dictionary

Method One: General method

The code is as follows:

# This method is convenient if you can spell the whole dictionary in advance
>>> D1 = {' name ': ' Bob ', ' Age ': 40}

Method Two: Dynamic creation

The code is as follows:

# This method is convenient if you need to create a field of the dictionary dynamically
>>> D2 = {}
>>> d2[' name '] = ' Bob '
>>> d2[' age '] = 40
>>> D2
{' Age ': +, ' name ': ' Bob '}

Method Three: dict--keyword form

The code is as follows:

# code is less, but the key must be a string type. Often used for function assignment
>>> D3 = dict (name= ' Bob ', age=45)
>>> D3
{' Age ': $, ' name ': ' Bob '}

Method Four: dict--key value Sequence

The code is as follows:

# This is useful if you need to build a sequence of key values, often in conjunction with the ZIP function
>>> D4 = dict ([' Name ', ' Bob '), (' Age ', 40)])
>>> D4
{' Age ': +, ' name ': ' Bob '}

Or

The code is as follows:

>>> D = dict ((' Name ', ' Bob '), (' Age ', 40))
>>> D
{' Bob ': +, ' name ': ' Age '}

Method Five: Dict--fromkeys method # If the values of the keys are the same, it is better in this way and can be initialized with Fromkeys.

The code is as follows:

>>> D5 = Dict.fromkeys ([' A ', ' B '],0)
>>> D5
{' A ': 0, ' B ': 0}

If the value of the key is not provided, the default is None

The code is as follows:

>>> D3 = Dict.fromkeys ([' A ', ' B '])
>>> D3
{' A ': None, ' B ': none}

The method of key value traversal in dictionary

The code is as follows:

>>> D = {' x ': 1, ' Y ': 2, ' Z ': 3} # Method One
>>> for key in D:
Print key, ' = = ', D[key]
y = 2
x = 1
z = 3
>>> for key, value in D.items (): # Method Two
Print key, ' = = ', value
y = 2
x = 1
z = 3

>>> for key in D.iterkeys (): # Method Three
Print key, ' = = ', D[key]
y = 2
x = 1
z = 3
>>> for value in D.values (): # method Four
Print value
2
1
3
>>> for key, value in D.iteritems (): # method Five
Print key, ' = = ', value

y = 2
x = 1
z = 3

Note: Using D.iteritems (), the D.iterkeys () method is much faster than no ITER.

Iv. One of the common uses of dictionaries instead of switch

In the C/c++/java language, there is a convenient function switch, for example:

The code is as follows:

public class Test {

public static void Main (string[] args) {
String s = "C";
Switch (s) {
Case "A":
System.out.println ("A");
Break
Case "B":
System.out.println ("B");
Break
Case "C":
System.out.println ("C");
Break
Default
System.out.println ("D");
}
}
}

To implement the same functionality in Python,
Method one is implemented with the IF, else statement, for example:

The code is as follows:

From __future__ Import Division

def add (x, y):
return x + y

def sub (x, y):
return x-y

def mul (x, y):
return x * y

def div (x, y):
return x/Y

def operator (x, y, sep= ' + '):
if Sep = = ' + ': Print add (x, y)
elif Sep = = '-': Print sub (x, y)
elif Sep = = ' * ': Print mul (x, y)
elif Sep = = '/': Print div (x, y)
Else:print ' Something wrong '

Print __name__

if __name__ = = ' __main__ ':
x = Int (raw_input ("Enter the 1st Number:"))
y = Int (raw_input ("Enter the 2nd Number:"))
s = raw_input ("Enter operation here (+-*/):")
Operator (x, y, s)

Method two, using a dictionary to skillfully implement the same switch function, such as:

The code is as follows:

#coding =GBK

From __future__ Import Division

x = Int (raw_input ("Enter the 1st Number:"))
y = Int (raw_input ("Enter the 2nd Number:"))

def operator (O):
Dict_oper = {
' + ': lambda x, y:x + y,
'-': Lambda x, y:x-y,
' * ': lambda x, y:x * y,
'/': lambda x, y:x/y}
return Dict_oper.get (O) (x, y)

if __name__ = = ' __main__ ':
o = Raw_input ("Enter operation here (+-*/):")
Print operator (o)

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