Python格式处理

[TOC]

### 一.CVS表格
```python
import csv
villains = [
    ['Doctor', 'No'],
    ['Rosa', 'Klebb'],
    ['Mister', 'Big'],
    ['Auric', 'Goldfinger'],
    ['Ernst', 'Blofeld'],
    ]
with open('villains', 'wt') as fout: # 一个上下文管理器
    csvout = csv.writer(fout)
    csvout.writerows(villains)

#读取cvs
with open('villains', 'rt') as fin: # 一个上下文管理器
    cin = csv.reader(fin)
    villains = [row for row in cin] # 使用列表推导式
print(villains)

#读取成字典方式
with open('villains', 'rt') as fin:
    cin = csv.DictReader(fin, fieldnames=['first', 'last'])
    villains = [row for row in cin]

#将字典写入成标题在上面的方式
villains = [
  {'first': 'Doctor', 'last': 'No'},
  {'first': 'Rosa', 'last': 'Klebb'},
  {'first': 'Mister', 'last': 'Big'},
  {'first': 'Auric', 'last': 'Goldfinger'},
  {'first': 'Ernst', 'last': 'Blofeld'},
  ]
with open('villains', 'wt') as fout:
  cout = csv.DictWriter(fout, ['first', 'last'])
  cout.writeheader()
  cout.writerows(villains)

with open('villains', 'rt') as fin: #重头读取文件
    cin = csv.DictReader(fin)
    villains = [row for row in cin]

```

### 二.xml
menu.xml
```python
<?xml version="1.0"?>
<menu>
  <breakfast hours="7-11">
    <item price="$6.00">breakfast burritos</item>
    <item price="$4.00">pancakes</item>
  </breakfast>
  <lunch hours="11-3">
    <item price="$5.00">hamburger</item>
  </lunch>
  <dinner hours="3-10">
    <item price="8.00">spaghetti</item>
  </dinner>
</menu>
```

```python
import xml.etree.ElementTree as et
tree = et.ElementTree(file='menu.xml')
root = tree.getroot()
root.tag

#tag是标签字符串，attrib是属性的一个字典
for child in root:
    print('tag:', child.tag, 'attributes:', child.attrib)
    for grandchild in child:
        print('\ttag:', grandchild.tag, 'attributes:', grandchild.attrib)

len(root) #菜单选择数目
len(roo[0]) #早餐项的数目
```

### 三.json
json字符串
```python
menu = \
    {
    "breakfast": {
        "hours": "7-11",
        "items": {
            "breakfast burritos": "$6.00",
            "pancakes": "$4.00"
            }
        },
    "lunch" : {
        "hours": "11-3",
        "items": {
            "hamburger": "$5.00"
            }
        },
    "dinner": {
        "hours": "3-10",
        "items": {
            "spaghetti": "$8.00"
            }
        }
    }
```

```python
import json
menu_json = json.dumps(menu)
menu_json

menu2 = json.loads(menu_json) #解析成python结构

import datetime
    now = datetime.datetime.utcnow()
json.dumps(now) #无法转换，因为标准json没有定义日期

#转换
now_str = str(now)
json.dumps(now_str) #可以转换了

from time import mktime
now_epoch = int(mktime(now.timetuple()))
json.dumps(now_epoch) #可以转换epoch值

class DTEncoder(json.JSONEncoder): #继承重载default方法
    def default(self, obj):
        # isinstance()检查obj的类型
        if isinstance(obj, datetime.datetime):
            return int(mktime(obj.timetuple()))
        # 否则是普通解码器知道的东西：
        return json.JSONEncoder.default(self, obj)
json.dumps(now, cls=DTEncoder)
```

### 四.yml
```python
import yaml
with open('mcintyre.yaml', 'rt') as fin:
    text = fin.read()
data = yaml.load(text)
data['details']
len(data['poems'])

data['poems'][1]['title'] #获得第二行
```

### 五.配置文件
```python
[english]
greeting = Hello

[french]
greeting = Bonjour

[files]
home = /usr/local

# 简单的插入：
bin = %(home)s/bin
```

```python
import configparser
cfg = configparser.ConfigParser()
cfg.read('settings.cfg')
cfg['french']
cfg['french']['greeting']
cfg['files']['bin']

#返回节点列表
config.sections()

#指定节点下的
config.options(section)
```
### 六.数据库
```python
连接数据库，包含参数用户名、密码、服务器地址
connect()

创建一个cursor对象来管理查询
cursor()

对数据库执行一个或多个SQL命令
execute() 和 executemany()

得到execute之后的结果
fetchone()、fetchmany() 和 fetchall()

import sqlite3
conn = sqlite3.connect('enterprise.db')
curs = conn.cursor()
curs.execute('''CREATE TABLE zoo
    (critter VARCHAR(20) PRIMARY KEY,
    count INT,
    damages FLOAT)''')

curs.execute('INSERT INTO zoo VALUES("duck", 5, 0.0)') #新增动物
curs.execute('INSERT INTO zoo VALUES("bear", 2, 1000.0)')

ins = 'INSERT INTO zoo (critter, count, damages) VALUES(?, ?, ?)'
curs.execute(ins, ('weasel', 1, 2000.0)) #更安全的插入数据方法

curs.execute('SELECT * FROM zoo') #获取数据
curs.fetchall()

curs.execute('SELECT * from zoo ORDER BY count') #按照count排序
curs.fetchall()

curs.execute('''SELECT * FROM zoo WHERE #哪种动物花费最多
    damages = (SELECT MAX(damages) FROM zoo)''')

curs.close() #打开后要关闭
```

![](/media/202104/2021-04-23_085444.png)