**Xiang Wang @ 2017-04-21 10:48:07**

* [official reference](https://docs.python.org/3/library/csv.html)

#### Module Contents

#### Dialects and Formatting Parameters

```python
class MyDialect(Dialect):
    """示例自定义格式"""
    delimiter = ";"
    quotechar = "%"
    quoting = QUOTE_ALL
    lineterminator = "end\r\n"
```

#### csv.DictReader

    file = open('filename.csv')
    reader = csv.DictReader(file)
    reader.fieldnames
    >>> ['number', 'name', 'tel']
    for row in reader:
        print(row) >>> {'tel': '', 'name': 'company', 'number': 'No. 1'}


#### [dictwriter](https://docs.python.org/3/library/csv.html#csv.DictWriter)
* example

```python
import csv
with open('names.csv', 'w') as csvfile:  # 也可以用a模式，继续写入。但是要注意fieldnames需要务必顺序正确
    fieldnames = ['first_name', 'last_name']
    writer = csv.DictWriter(csvfile, fieldnames=fieldnames)
    writer.writeheader()
    writer.writerow(<dict>)
    writer.writerows([<dict1>, <dict2>])
```


* `csv.DictWriter`
    * extrasaction = 'raise' | 'ignore' raise ValueError or not if there is another keys in `<dict>` data
    * delimiter=',' the delimiter between columns
* Attention
    * If a key is missing in the dict, the data will set blank instead of raise exception