[Python] study notes 4-tuples

What is a tuple?

A tuple is a sequence, just like a list. The difference between tuples and lists is that, unlike lists (mutable), tuples cannot be changed (immutable).
Tuples use brackets (), and lists use square brackets [].

1. Initialize tuples and assign values

#两种方法都可以初始化
emptyTuple=()
emptyTuple1=tuple()

#两种方法都可以赋值
emptyTuple=(1,2,3,4)
emptyTuple1=1,2,3,4

print(emptyTuple)
print(emptyTuple1)

result:

It is important to remember

If you want to create a tuple that contains only one value, you need to add a comma after the item.

#只有一个值的话后面要加逗号
tup=('a',)
tup1='a',

#如果没有逗号，那它是一个string不是一个元组了
notTuple=('a')

print(tup)
print(tup1)
print(notTuple)

Result:

2. Visit value

tun=(2,3,4,5)
print(tun[0])#索引正向从0开始
print(tun[-4])#索引负向从最后一个-1开始倒数

Results:

3. Split tuples

tun=(2,3,4,5)
print(tun[0:2])
print(tun[:3])
print(tun[-3:-1])

Result:

4. The tuple cannot be changed

tun=(2,3,4,5)
tun[0]='fish'

result:

Even if the tuple is immutable, a part of the existing tuple can be used to create a new tuple

tun=(2,3,4,5)
tun1=(6,7,8,9)
tunall=tun+tun1
print(tunall)

Results:

5. Tuple method

animals=('pig','pig','cat',1)

#返回索引
print('pig first index: ',animals.index('pig'))
print('cat first index: ',animals.index('cat'))

#计数
print(animals.count('pig'))

result:

6. Iterate over tuples

animals=('pig','pig','cat',1)

for item in animals:
    print(item)

for item in ('a','b','c'):
    print(item)

Results:

7. Tuple unpacking Tuples
are very useful for sequence unpacking

x,y=(7,10)
print(x)
print(y)

print("Value of x is {},the value of y is {}".format(x,y))

Result:

8. Enumeration The
enumeration function returns a tuple containing the count of each iteration (starting from the default of 0) and the value obtained by the iteration sequence

friends = ('Steve', 'Rachel', 'Michael', 'Monica')
for index, friend in enumerate(friends):
    print(index,friend)
    print(index)
    print(friend)


for index in enumerate(friends):
    print(index)

result:

Advantages of tuples over lists

Lists and tuples are standard Python data types used to store values ​​in sequences. Tuples are immutable, while lists are mutable.

Here are some other advantages of tuple lists:

**Groups are faster than lists. **If you are going to define a set of constant values, then all you will do is iterate over it, using tuples instead of lists. The performance difference can be measured in part using the timeit library, which allows you to time your Python code. The following code runs the code 1 million times for each method and outputs the total time spent (in seconds).

import timeit 
print('Tuple time: ', timeit.timeit('x=(1,2,3,4,5,6,7,8,9,10,11,12)', number=1000000))
print('List time: ', timeit.timeit('x=[1,2,3,4,5,6,7,8,9,10,11,12]', number=1000000))

Result:

Tuples can be used as dictionary keys : Some tuples can be used as dictionary keys (especially tuples containing immutable values, such as strings, numbers, and other tuples). Lists can never be used as dictionary keys, because lists are not immutable.

bigramsTupleDict = {
    
    ('this', 'is'): 23,
                    ('is', 'a'): 12,
                    ('a', 'sentence'): 2}

print(bigramsTupleDict)

Result:

but the list does not work

bigramsListDict = {
    
    ['this', 'is']: 23,
                   ['is', 'a']: 12,
                   ['a', 'sentence']: 2}

print(bigramsListDict)

Result:

Tuples can be values ​​in the collection

graphicDesigner = {
    
    ('this', 'is'),
                   ('is', 'a'),
                   ('a', 'sentence')}
print(graphicDesigner)

Result: The

list cannot be a value in the collection:

graphicDesigner = {
    
    ['this', 'is'],
                   ['is', 'a'],
                   ['a', 'sentence']}
print(graphicDesigner)

result: