Python introductory notes--from list to sequence

(unfinished, catalog only)

the list

simple data type
container data type

• list<class 'list'>
• tuple<class 'tuple'>
• dictionary<class 'dict'>
• collection<class 'set'>
• string<class 'str'>

List definition and creation

A list is an ordered collection with no fixed size and can store any number of Python objects of any type. The syntax is [element 1, element 2, ..., element n]

• create a normal list
• Use range() to create a list
• Create lists using comprehensions

Note: x = [a] * 4In the operation, only 4 references to the list are created, so once achanged, x4 of them awill also change accordingly.

• create a mixed list
• create an empty list

Adding, deleting, and obtaining elements in the list

`
Add:

• list.append(obj) 在列表末尾添加新的对象，只接受一个参数，参数可以是任何数据类型，被追加的元素在The original structure type is maintained in list`.
• Note the difference between append()and extend().
• list.extend(seq)Append multiple values ​​from another sequence at once to the end of a list (extending the original list with the new list)
• list.insert(index, obj)Insert at numbered indexposition obj.

delete:

• list.remove(obj)removes the first occurrence of a value in a list
• list.pop([index=-1])Remove an element in the list (the last element by default), and return the value of the element
• del var1[, var2 ……]Delete single or multiple objects.
• If you delete an element from a list and don't use it in any way, use the del statement; if you want to continue using it after deleting an element, use a method pop().

Get: Exercise Example
Example 1

x = ['Monday', 'Tuesday', 'Wednesday', ['Thursday', 'Friday']]
print(x[0], type(x[0]))  # Monday <class 'str'>
print(x[-1], type(x[-1]))  # ['Thursday', 'Friday'] <class 'list'>
print(x[-2], type(x[-2]))  # Wednesday <class 'str'>

Example 2

x = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
print(x[3:])  # ['Thursday', 'Friday']
print(x[-3:])  # ['Wednesday', 'Thursday', 'Friday']

Example 3

week = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
print(week[:3])  # ['Monday', 'Tuesday', 'Wednesday']
print(week[:-3])  # ['Monday', 'Tuesday']

example 4

week = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
print(week[1:3])  # ['Tuesday', 'Wednesday']
print(week[-3:-1])  # ['Wednesday', 'Thursday']

example 5

week = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
print(week[1:4:2])  # ['Tuesday', 'Thursday']
print(week[:4:2])  # ['Monday', 'Wednesday']
print(week[1::2])  # ['Tuesday', 'Thursday']
print(week[::-1])  
# ['Friday', 'Thursday', 'Wednesday', 'Tuesday', 'Monday']

example 6

eek = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
print(week[:])  
# ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']

Example 7 deep and shallow copy

list1 = [123, 456, 789, 213]
list2 = list1
list3 = list1[:]

print(list2)  # [123, 456, 789, 213]
print(list3)  # [123, 456, 789, 213]
list1.sort()
print(list2)  # [123, 213, 456, 789] 
print(list3)  # [123, 456, 789, 213]

list1 = [[123, 456], [789, 213]]
list2 = list1
list3 = list1[:]
print(list2)  # [[123, 456], [789, 213]]
print(list3)  # [[123, 456], [789, 213]]
list1[0][0] = 111
print(list2)  # [[111, 456], [789, 213]]
print(list3)  # [[111, 456], [789, 213]]

Common Operators for Lists

• Equal operator:==
• join operator+
• repeat operator*
• membership operator in,not in

「等号 ==」, returns only when the member and member position are the same True.

There are two ways to splicing lists, using "plus sign +" and "multiplication sign *".

Other methods for lists

• list.count(obj)Count the number of times an element appears in a list
• list.index(x[, start[, end]])Find the index position of the first occurrence of a value in a list
• list.reverse()reverse list element
• list.sort(key=None, reverse=False)Sort the original list.

In addition
key --, it is mainly an element used for comparison, and has only one parameter. The parameter of the specific function is taken from the iterable object, and an element in the iterable object is specified for sorting.
reverse --collation, reverse = Truedescending, reverse = Falseascending (default).
This method has no return value, but sorts the objects in the list.

tuple

Create and access, update and delete a tuple

Operators related to tuples

built-in method

unpack tuple

---

string

Commonly used escape characters:
\\backslash symbol
\', single quote,
\"double quote,
\nnewline,
\thorizontal tab (TAB),
\rcarriage return

Definition of string

Slicing and concatenating strings

Common built-in methods for strings

string formatting

dictionary

Mutable and immutable types

dictionary definition

Create and access dictionaries

built-in methods of dictionaries