The difference between lists, tuples, sets, and dictionaries in python

1. List

1. An ordered collection of any objects
A list is a set of values ​​of any type, in a certain order The combined
2. Read through offset
The values ​​​​that make up the list are called elements (Elements). Each element is marked with an index, the first index is 0, and the functions of the sequence can be realized
3. Variable length, heterogeneous and arbitrary nesting
The elements in the list can be of any type, even List type, that is to say, lists can be nested
4. Variable sequence
Supports indexing, slicing, merging, deletion and other operations, they all modify the list in place
5. Object reference array
The list can be treated as an ordinary array. Whenever a reference is used, Python will always point the reference to an object, so the program only needs to handle the operation of the object. When assigning an object to a data structure element or variable name, Python will always store a reference to the object, rather than a copy of the object

2. Tuple

1. An ordered collection of arbitrary objects
Same as a list
2. Access via offset
Same as a list
3. Belongs to an immutable sequence type
Similar to a string, However, tuples are immutable and do not support any in-place modification operations in the list or any method calls
4. Fixed length, heterogeneity, arbitrary nesting
Fixed length means that tuples are immutable. The length is fixed if it is not copied, and the others are the same as the list
5. The array of object references
is similar to the list, the ancestor is the array of object references

Compared with list
1. The list operation is fast
2. "Write-protect" the data
3. Can be used in string formatting
4. Can be used as the key of the dictionary

3. Dictionary

1. Read by key instead of offset
The dictionary is an associative array, a collection of objects indexed by keywords, using key-value (key-value) Storage and search speed
2. An unordered collection of arbitrary objects
The items in the dictionary have no specific order, symbolized by "keys"
3. Variable length, heterogeneity, arbitrary nesting
Same as a list, nesting can include lists and other dictionaries, etc.
4. Belongs to a variable mapping type
Because it is unordered, sequence operations cannot be performed, but it can be modified remotely and mapped to values ​​through keys . Dictionaries are the only built-in mapping type (objects that map keys to values)
5. Object reference table
Dictionaries store object references, not copies, just like lists. The key of the dictionary cannot be changed, and the list cannot be used as the key. Strings, primitives, integers, etc. can be compared with the list. The dict has the following characteristics:

1. The speed of search and insertion is extremely high Fast and will not increase with the increase of keys

2. It takes up a lot of memory and wastes a lot of memory
On the contrary for list:
1. The time for searching and inserting increases with the increase of elements
2. It takes up little space and wastes very little memory
So, dict is a way to exchange space for time

4. Collection

1 . is a set of keys, but does not store values, and keys cannot be repeated

To create a set, you need to provide a list as the input set, s = set([1,2,3]), note that the incoming The parameter [1, 2, 3] is a list, and the displayed set([1, 2, 3]) only tells you that there are 3 elements 1, 2, and 3 inside this set. The displayed [ ] does not mean that this is A list

2. Repeated elements are automatically filtered in the set
set can be regarded as a collection of unordered and non-repeating elements in the mathematical sense. Therefore, two sets can be intersection and union in the mathematical sense. Waiting for operations

There is another kind of collection called forzenset(), which is a frozen collection. It is immutable and has a hash value. The advantage is that it can be used as the key of a dictionary or as an element of other collections. The disadvantage is that once created, it cannot be changed. There is no add or remove method.

Comparison with dict

1. The only difference between .set and dict is that the corresponding value is not stored.

2. The principle of set and dict Likewise, variable objects cannot be placed because it is impossible to determine whether two variable objects are equal, and there is no guarantee that "there will be no duplicate elements" inside the set

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