Keywords: Python

# Basic data types and built-in methods (2)

### I. built in method of list

• Count: count the number of specified elements in the current list
```s1 = ['y', 'a', 'f', 'e', 'n', 'g', '6', '6', '6']
s1.count('6')
print(s1.count('6'))
>>>3```
• Index: get the index of the current element, and specify the search range
```s1 = ['y', 'a', 'f', 'e', 'n', 'g', '6', '6', '6']
s1.index('6')
print(s1.index('6'))
>>>6
s1.index("6", 7)
print(s1.index("6", 7))
>>>7```
• Sort: sort, default reverse=False, i.e. ascending sort
```s1 = [1, 2, 5, 6, 7, 8, 9]
s1.sort()
print(s1)
>>>[1, 2, 5, 6, 7, 8, 9]

s1 = [1, 2, 5, 6, 7, 8, 9]
s1.sort(reverse=True)
print(s1)
>>>[9, 8, 7, 6, 5, 2, 1]```
• sorted:python's built-in sorting. When sorting, a new list will be produced, and the original data will not change
```s1 = [1, 2, 5, 6, 7, 8, 9]
a = sorted(s1)
print(a)
>>>[1, 2, 5, 6, 7, 8, 9]

s1 = [1, 2, 5, 6, 7, 8, 9]
a = sorted(s1, reverse=True)
print(a)
>>>[9, 8, 7, 6, 5, 2, 1]```
• Clear: clear all data in the list
```s1 = [1, 2, 5, 6, 7, 8, 9]
s1.clear()
print(s1)
>>>[]```
• Queues and stacks
```'''
//Queue: first in, first out
l1 = []
l1.append(1)
l1.append(2)
l1.append(3)
print(l1)
>>>[1,2,3]
l1.pop[0]
print(l1)
>>>[2,3]
l1.pop[0]
print(l1)
>>>[3]
l1.pop[0]
print(l1)
>>>[]

//Stack: first in first out
l1 = []
l1.append(1)
l1.append(2)
l1.append(3)
print(l1)
>>>[1,2,3]
l1.pop()
print(l1)
>>>[1,2]
l1.pop()
print(l1)
>>>[1]
l1.pop()
print(l1)
>>>[]

'''```
• Summary

The list can store multiple values, orderly (ordered if there is index), variable

### Two, Yuan Zu

• Definition and usage
```#Purpose: store multiple values of different types (variable types are not allowed)
#Definition method: data is stored in parentheses. Data and data are separated by commas. (value cannot be changed)
#When defining a container type, if there is only one value in it, add a comma after the value (very important)
#If it is not added in the tuple, it is a string```
• common method
```"""
1,Index value (positive, negative)
2,Index slice
3,Member operation in ，not in
4,len()
"""
1,Index value
t1 = ('y', 'a', 'f', 'e', 'n', 'g')
print(t1[1])
>>>a

t1 = ('y', 'a', 'f', 'e', 'n', 'g')
print(t1[-2])
>>>n

2,Index slice
t1 = ('y', 'a', 'f', 'e', 'n', 'g')
print(t1[2:])
>>>('f', 'e', 'n', 'g')

3,Member operation
t1 = ('y', 'a', 'f', 'e', 'n', 'g')
print('a' in t1)
>>>True

4,len()
t1 = ('y', 'a', 'f', 'e', 'n', 'g')
print(len(t1))
>>>6```
• Summary

Orderly, multiple values can be saved, immutable

### Three, dictionary

• Definition and definition method
```Definition mode:Data is stored through braces, through key:value To define key value pair data, each key value pair is separated by commas
key:Must be an immutable type
value: Can be any type

//Three definitions:
1,important
d1 = {
'name': 'yafeng',
'age': '18',
'hobby': 'study'
}
print(d1)
>>>{'name': 'yafeng', 'age': '18', 'hobby': 'study'}
2,important
d2 = dict({'name': 'yafeng', 'age': '18', 'hobby': 'study'})
print(d2)
>>>{'name': 'yafeng', 'age': '18', 'hobby': 'study'}
3,Can understand
l1 = ['name', "age", "hobby"]
l2 = ['yafeng', 18, "study"]
z1 = zip(l1, l2)
print(dict(z1))
>>>{'name': 'yafeng', 'age': 18, 'hobby': 'study'}
```
• Priority method
```"""
1. Priority:
1. Take the value according to the key:value mapping relationship (can be saved or desirable)
2. Member operation in, not in. Default key
3. len() -- get the number of key value pairs in the current dictionary
"""```
• Built in method get
```get:Get assigned key If the value does not exist, the default value is None，The second parameter can be used to modify the content returned by default
d1 = {
'name': 'yafeng',
'age': '18',
'hobby': 'study'
}
print(d1.get('name'))
>>>yafeng```
• keys,values,items
```keys Return all key
values Return all values
items Return all key value pairs, return value is list
d1 = {
'name': 'yafeng',
'age': '18',
'hobby': 'study'
}
for key in d1.keys():
print(key)
for value in d1.values():
print(value)
for key, value in d1.items():
print(key, value)
key, value = ("name", 'age')
>>>name
age
hobby
yafeng
18
study
name yafeng
age 18
jhobby study```
• pop
```pop Appoint key To delete, return to the corresponding value value
a = d1.pop('age')
print(d1)
print(a)
>>>{'name': 'yafeng', 'hobby': 'study'}
>>>18```
• popitem
```A key value pair will pop up randomly. If there is a return value, the return value is a primitive ancestor
d1.popitem()
print(d1)
>>>{'name': 'yafeng', 'age': '18'}```
• update
```Replace old dictionary with new one
d1.update({'gender': 'male'})
print(d1)
>>>{'name': 'yafeng', 'age': '18', 'hobby': 'study', 'gender': 'male'}```
• fromkeys
```To produce a new dictionary, take each element in the first parameter (iteratable object) as the key and the second parameter as the value to form a new dictionary
print(dict.fromkeys([1, 2, 3], ['ke', 'k1']))
>>>{1: ['ke', 'k1'], 2: ['ke', 'k1'], 3: ['ke', 'k1']}```
• setdefault
```key If there is no new key value pair, return to new if there is a return value value，key There is a corresponding value
print(d1.setdefault('height', '1.77'))
print(d1)
>>>1.77
>>>{'name': 'yafeng', 'age': '18', 'hobby': 'study', 'height': '1.77'}
```

### Four, set

```# Purpose: de duplication and relation operation
# Definition method: data is stored by braces, and each element is separated by commas
# To define an empty set, you must use set() to define
# l1 = []
# s1 = ""
# d1 = {}
# ss1 = set()
# Common methods:

"""
//Consortium:
//Intersection:
//Difference sets:
//Symmetric difference set:^
"""

"""
1,Two identical elements are not possible in a collection
"""

python_student = {'egon', 'jason', 'tank', 'owen', 'egon'}
linux_student = {'frank', 'alex', 'egon'}
go_student = {'egon'}

print(python_student)
# print(python_student | linux_student)
# print(python_student & linux_student)
# print(python_student - linux_student)
# print(linux_student - python_student)
# print(python_student ^ linux_student)
# print(python_student > go_student)
# print(python_student < linux_student)

# l1 = [1, 2, 3, 1, 2, 9, 1, 5, 6, 7]
# print(l1)
#
# s1 = set(l1)
# print(s1)
# print(type(s1))
# l2 = list(s1)
# print(l2)
# print(type(l2))

for i in python_student:
print(i)```
• Summary

Unordered, variable, store multiple values

### Five, summary

```"""
Save one: integer, floating point, string
Store multiple values: list, tuple, dictionary, set

Variable or immutable:
Variable:; list, dictionary, set
Immutable: integer, floating point, string, tuple

Ordered or unordered:
Order: string, list, tuple
Disorder: dictionary, set

Occupied space:
Dictionaries
list
tuple
aggregate
Character string
Numeric type
"""```

Posted by ICEcoffee on Wed, 06 Nov 2019 01:44:04 -0800