python array

1. There are three types of Python arrays:
1. List linked list array, elements can be dynamically added through specific methods after initialization.
Definition method: arr = [element]
2. Tuple is a fixed array. Once defined, the number of elements cannot be changed.
Definition method: arr = (element)
3. Dictionary dictionary array, which is a Hash array.
Definition method: arr = {element key:value} or arr = dict(element key:value)
Contains two parts: key and value. The key is of Integer or string type, and the value is of any type.
2. The following is a detailed description of the usage methods and techniques of these arrays:
1. List linked list array
(1) Initialization when defining
    arr = [1, 2, [1, 2, 3]]
  (2) Not when defining Initialization
          One-dimensional array: arr = []
          Multi-dimensional array: arr = [i for i in range(10), 1,[]]
      #Note: i for in xx must be placed in the first position, otherwise it will be Define i first.
(3) Deleting an array and getting multiple values ​​
You can use start:end to represent an interval in the array (i >= start and i < end)
del arr[0]
del arr[0:2]
newarr = arr[0:2] (4) Traverse the array
for k, v in enumerate(arr):
print k, v
#When you want to traverse both the index and the elements of a list or array, you can use the enumerate function
(5) Add elements:
One-dimensional: arr.append('aaa')
Two-dimensional: arr[0].append('aaa')
If you want to insert at the specified index position, use arr.insert(index, value
In addition, there is a special usage: ARR += [Array Element]
In the absence of designated bidding, it allows += to increase the array elements.
        * operator, such as arr*4
      (6) Method
                                                                                        using     using ’ ’s ’ using ’s ’ using ’ using ’s ‐ ‐  ‐  ‐   ‐                                                                             to be Remove from
        L.remove(var) #Delete the first occurrence of the element
      L.count(var) #The number of times this element appears in the list
      L.index(var) #The position of this element, none Then throw an exception
          L.extend(list) #Append the list, that is, merge the list to L
        L.sort() # Sort
              L.reverse() # Reverse order
    (7) Copy
      L1 = L                                                                      Alias, in C terms, means that the pointer address is the same, and the operation on L1 is the operation on L. This is how the function parameters are passed L1 = L[:] #L1 is a clone of L, that is, another copy.
2.Tuple fixed array
(1) Initialize when defining
arr = ("a", "b", "c", "d", "e")
(2) Get the value
Print arr[0], arr[-4:-1],arr[-1],arr[1:4]
 (3) Traverse the array
    for k,v in enumerate(arr):
                                                           . = list( t )
                                                                                                                                                                                                                 . , 'c': 'hello'}
How to give a key corresponding to several values.
           Dictionaries can correspond to many meanings, and of course Key can also correspond to many values ​​
Although Python itself cannot perform multiple assignments to dictionary keys, we can use the list method.
      arr = {'server': ['yp.geekso.com','geekso.com'], 'database': 'mysql'}
                                                                                                using   using using   using   using   using using       ‐                                       using   using   using   using   using       using using ‐ ‐ ‐ ‐ ‐d.get(key, 0) #Same as dict[ key], if there are more than one, the default value, 0, will be returned. [] If not, an exception will be thrown
      D.has_key(key) #Return TRUE if the key exists, otherwise FALSE
      D.keys() #Return a list of dictionary keys
      D.values() #Output all values ​​
      D.items( ) #Return a list of tuples, each tuple contains a key-value pair
      D.update(dict2) #Add a merged dictionary
      D.popitem() #Get a pair and delete it from the dictionary . If it is empty, an exception will be thrown
        setdefault(key [,dummvalue])
      #Has similar behavior to the get method.
        #If the key is not in the dictionary and dummvalue is specified, insert the key (key)
            # and the specified value (dummvalue) into the dictionary,
        #If dummvalue is not specified, the value is None
                                        D.clear() #                                                      Dictionary, same as del dict
      D.copy() #Copy dictionary
        D.cmp(dict1,dict2) #Compare dictionaries, (the priority is the number of elements, key size, key value size)
 (3) Copy
    dict1 = dict #Alias ​​
dict2=dict.copy() #Clone, that is, another copy.