Detailed explanation of Python tuple operations

1. Create a tuple

tup1 = ('physics', 'chemistry', 1997, 2000);
tup2 = (1, 2, 3, 4, 5 );
tup3 = "a", "b", "c", "d";

Create an empty tuple

tup1 = ();

When a tuple contains only one element, you need to add a comma after the element to eliminate ambiguity

tup1 = (50,);

Tuples are similar to strings. The subscript index starts from 0 and can be intercepted, combined, etc.
2. Access tuples
Tuples can use subscript indexes to access the values ​​in the tuples, as shown in the following example:

#!/usr/bin/python
tup1 = ('physics', 'chemistry', 1997, 2000);
tup2 = (1, 2, 3, 4, 5, 6, 7 );
print "tup1[0]: ", tup1[0]
print "tup2[1:5]: ", tup2[1:5]
#以上实例输出结果：
#tup1[0]:  physics
#tup2[1:5]:  [2, 3, 4, 5]

3. Modify the element values ​​in the tuples
Modification is not allowed, but we can connect and combine tuples, as shown in the following example:

#!/usr/bin/python
tup1 = (12, 34.56);
tup2 = ('abc', 'xyz');
# 以下修改元组元素操作是非法的。
# tup1[0] = 100;
# 创建一个新的元组
tup3 = tup1 + tup2;
print tup3;
#以上实例输出结果：
#(12, 34.56, 'abc', 'xyz')

4. Delete tuples
The element values ​​in the tuple are not allowed to be deleted, but we can use del statement to delete the entire tuple, as shown in the following example:

#!/usr/bin/python
tup = ('physics', 'chemistry', 1997, 2000);
print tup;
del tup;
print "After deleting tup : "
print tup;

#After the above example tuple is deleted, the output variable will have an exception message, and the output is as follows:
#('physics', 'chemistry ', 1997, 2000)
#After deleting tup :
#Traceback (most recent call last):
# File "test.py", line 9, in
# print tup;
#NameError: name 'tup' is not defined[/code]
5. Tuple operator
Like strings, tuples can be operated using the + and * signs. This means that they can be combined and copied, resulting in a new tuple.

6. Tuple index, interception
Because the tuple is also a sequence, we can access the element at the specified position in the tuple, or intercept the index. A section of elements, as shown below:
Tuple:

L = ('spam', 'Spam', 'SPAM!')

7. No closing delimiter
Any unsigned object separated by commas, defaults to a tuple, as shown in the following example:

#!/usr/bin/python
print 'abc', -4.24e93, 18+6.6j, 'xyz';
x, y = 1, 2;
print "Value of x , y : ", x,y;

The above examples allow results:

abc -4.24e+93 (18+6.6j) xyz
Value of x , y : 1 2

8. Tuple built-in functions
Python tuples include the following built-in functions
1. cmp(tuple1, tuple2): compare two Tuple element.
2. len(tuple): Calculate the number of tuple elements.
3. max(tuple): Returns the maximum value of the element in the tuple.
4. min(tuple): Returns the minimum value of the element in the tuple.
5. tuple(seq): Convert the list into a tuple.

##9. Another interpretation

tuple is very similar to list, but once initialized, tuple cannot be modified. For example, the names of classmates are also listed:

>>> classmates = ('Michael', 'Bob', 'Tracy')

Now, the classes tuple cannot be changed, and it does not have methods such as append() and insert(). Other methods of obtaining elements are the same as lists. You can use classes[0] and classes[-1] normally, but they cannot be assigned to other elements.

What is the significance of immutable tuple? Because tuples are immutable, the code is safer. If possible, use tuple instead of list.
Traps of tuple: When you define a tuple, the elements of the tuple must be determined at the time of definition, for example:

>>> t = (1, 2)
>>> t
(1, 2)

If you want to define an empty tuple, you can write ():

>>> t = ()
>>> t
()

However, to define a tuple with only 1 element, if you define it like this:

>>> t = (1)
>>> t
1

What you define is not a tuple, but the number 1! This is because brackets () can represent both tuples and parentheses in mathematical formulas, which creates ambiguity. Therefore, Python stipulates that in this case, calculations are performed according to parentheses, and the calculation result is naturally 1.

So, a comma must be added when defining a tuple with only 1 element to eliminate ambiguity:

>>> t = (1,)
>>> t
(1,)

Python will also add a comma when displaying a tuple with only 1 element to avoid you Misunderstood as parentheses in the sense of mathematical calculations.

Let's look at a "variable" tuple:

>>> t = ('a', 'b', ['A', 'B'])
>>> t[2][0] = 'X'
>>> t[2][1] = 'Y'
>>> t
('a', 'b', ['X', 'Y'])

This tuple has three elements when it is defined, namely 'a', 'b' and a list. Doesn’t it mean that a tuple is immutable once it is defined? Why did it change later?

Don't worry, let's first take a look at the three elements contained in the tuple when it was defined:

When we put the elements 'A' and 'B of the list 'After changing to 'X' and 'Y', the tuple becomes:

On the surface, the elements of the tuple have indeed changed, but in fact, it is not the elements of the tuple that have changed. , but the elements of list. The list pointed to by the tuple at the beginning has not changed to another list. Therefore, the so-called "unchanged" of the tuple means that each element of the tuple will never change. That is, if it points to 'a', it cannot be changed to point to 'b'. If it points to a list, it cannot be changed to point to other objects, but the list it points to is variable!

After understanding "the pointer does not change", how to create a tuple whose content does not change? Then it must be ensured that each element of the tuple itself cannot be changed.

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