#There are four basic Python tutorials in this series, and this article is the second one.
Tuple is very similar to list, but tuple is immutable, that is, tuple cannot be modified. Tuple is defined by items separated by commas in parentheses.
Advantages: tuple is faster than list Fast; 'write-protect' data that does not need to be modified can make the code safer
tuple and list can be converted to each other, using the built-in functions list() and tuple().
l = [1, 2, 3] print( l )# [1, 2, 3]t = tuple(l) print(t) # (1, 2, 3)l = list(t)print (l) #[1, 2, 3]复制代码
The most common use of tuples is in print statements, as in the following example:
name = "Runsen"age = 20print( "Name: %s; Age: %d") % (name, age)# Name: Runsen; Age: 20复制代码
The function is as follows:
Returns the number of elements in the tuple whose value is value
t = (1, 2, 3, 1, 2, 3)print (t.count(2) )# 2复制代码
Returns the index of the first occurrence of value in the list, if not, an exception occurs ValueError
t = (1, 2, 3, 1, 2, 3) print( t.index(3) )# 2try: print (t.index(4))except ValueError as V: print(V) # there is no 4 in tuple复制代码
Dictionary by key Composed of value pairs, the key must be unique;
eg: d = {key1:value1, key2:value2};
The empty dictionary is represented by {}; dictionary The key-value pairs in are not in order. If you want a specific order, you need to sort them before use;
d[key] = value, if it already exists in the dictionary key, then assign it the value value, otherwise add a new key-value pair key/value;
use del d [key] You can delete key-value pairs; to determine whether there is a key in the dictionary, you can use in or not in;
d = {}
d["1"] = "one"d["2"] = "two"d["3"] = "three"del d["3"]for key, value in d.items(): print ("%s --> %s" % (key, value))#1 --> one#2 --> two复制代码The dict function is as follows:
Delete all elements in the dictionary
d1 = {"1":"one", "2":"two"}
d1.clear()print (d1 )# {}复制代码Return a copy of the dictionary (shallow copy )
d1 = {"1":"one", "2":"two"}
d2 = d1.copy()
print( d2 )#{'1': 'one', '2': 'two'}print(d1 == d2) # Trueprint(d1 is d2) # False复制代码Shallow copy values are the same, but the objects are different and the memory addresses are different.
Create and return a new dictionary, using the elements in the sequence seq as the keys of the dictionary, and val is all the keys of the dictionary Corresponding initial value (default is None)
l = [1, 2, 3]
t = (1, 2, 3)
d3 = {}.fromkeys(l)print (d3) #{1: None, 2: None, 3: None}d4 = {}.fromkeys(t, "default")
print(d4) #{1: 'default', 2: 'default', 3: 'default'}复制代码Returns the corresponding value of the key key in the dictionary dict, if it does not exist in the dictionary If this key is used, the default value is returned (the default value is None)
d5 = {1:"one", 2:"two", 3:"three"}print (d5.get(1) )#oneprint (d5.get(5)) #Noneprint (d5.get(5, "test") )#test复制代码Determine whether there is a key key in the dictionary
d6 = {1:"one", 2:"two", 3:"three"}
print( d6.has_key(1) ) #Trueprint (d6.has_key(5)) #False复制代码Returns a list containing tuples of (key, value) pairs in the dictionary
d7 = {1:"one", 2:"two", 3:"three"}for item in d7.items(): print (item)#(1, 'one')#(2, 'two')#(3, 'three')for key, value in d7.items(): print ("%s -- %s" % (key, value))#1 -- one#2 -- two#3 -- three复制代码Returns a list containing all the keys in the dictionary
d8 = {1:"one", 2:"two", 3:"three"}for key in d8.keys(): print (key)#1#2#3复制代码Returns a list containing all the values in the dictionary
d8 = {1:"one", 2:"two", 3:"three"}for value in d8.values():
print( value)#one#two#three复制代码If the key key exists in the dictionary, delete it and return dict[key]. If it does not exist and no default value is given, a KeyError exception is raised.
d9 = {1:"one", 2:"two", 3:"three"}print (d9.pop(1) )#oneprint( d9) #{2: 'two', 3: 'three'}print( d9.pop(5, None)) #Nonetry:
d9.pop(5) # raise KeyErrorexcept KeyError, ke: print ( "KeyError:", ke) #KeyError:5复制代码Delete any key-value pair and return the key-value pair. If the dictionary is empty, an exception KeyError
d10 = {1:"one", 2:"two", 3:"three"}print (d10.popitem() ) #(1, 'one')print (d10) #{2: 'two', 3: 'three'}复制代码d = {1:"one", 2:"two", 3:"three"}print (d.setdefault(1)) #oneprint (d.setdefault(5)) #Noneprint( d) #{1: 'one', 2: 'two', 3: 'three', 5: None}print (d.setdefault(6, "six")) #sixprint (d) #{1: 'one', 2: 'two', 3: 'three', 5: None, 6: 'six'}复制代码d = {1:"one", 2:"two", 3:"three"}
d2 = {1:"first", 4:"forth"}
d.update(d2)print (d) #{1: 'first', 2: 'two', 3: 'three', 4: 'forth'}复制代码d = {1:"one", 2:"two", 3:"three"}for key, value in d.viewitems(): print ("%s - %s" % (key, value))#1 - one#2 - two#3 - three复制代码d = {1:"one", 2:"two", 3:"three"}for key in d.viewkeys():
print( key)#1#2#3复制代码d = {1:"one", 2:"two", 3:"three"}for value in d.viewvalues(): print (value)#one#two#three复制代码Index operator and slice operator
numbers = ["zero", "one", "two", "three", "four"] print (numbers[1] )# oneprint (numbers[-1] )# four#print( numbers[5]) # raise IndexErrorprint (numbers[:]) # ['zero', 'one', 'two', 'three', 'four']print (numbers[3:]) # ['three', 'four']print (numbers[:2]) # ['zero', 'one']print (numbers[2:4] )# ['two', 'three']print (numbers[1:-1] )# ['one', 'two', 'three'] 复制代码
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