marshmallow库的简单介绍

marshmallow库

marshmallow库是用来进行对象序列化(dump/dumps)和反序列化(load/loads)的处理的。

简单来说，就是将python里的object对象与list/dict，json字符串对象三者之间进行相互转换

• 序列化: 把变量从内存中变成可存储或传输的过程

作用

• Validate input data.
• Deserialize input data to app-level objects.
• Serialize app-level objects to primitive Python types.

使用

• 安装 pip install marshmallow

最基本的使用例子

from datetime import date
from marshmallow import Schema, fields
       
class User:
    def __init__(self, name, email):
        self.name = name
        self.email = email
        self.created_at = dt.datetime.now()
        
# 继承Schema，声明自己的类
class UserSchema(Schema):
    name = fields.Str()
    email = fields.Email()
    created_at = fields.DateTime()
    
    # 用于在使用load时把他反序列化为User object
    @post_load
    def make_user(self, data, **kwargs):
        return User(**data)
      
# 初始化schema类
schema = UserSchema()

# 初始化类
user = User(name="Monty", email="monty@python.org")

# 序列化。dumps可以转换为json字符串对象
result = schema.dump(user)
# {"name": "Monty",
#  "email": "monty@python.org",
#  "created_at": "2014-08-17T14:54:16.049594+00:00"}

# 反序列化。loads可以将json字符串对象转换为object或者字符串/列表
user_data = {
    "created_at": "2014-08-11T05:26:03.869245",
    "email": "ken@yahoo.com",
    "name": "Ken",
}
result = schema.load(user_data)
print(result)  # => <User(name='Ken')>

捕获异常

try:
    result = UserSchema().load({"name": "John", "email": "foo"})
except ValidationError as err:
    print(err.messages)  # => {"email": ['"foo" is not a valid email address.']}
    print(err.valid_data)  # => {"name": "John"}

可以验证的类型

AwareDateTime(format, *, default_timezone, …)	A formatted aware datetime string.
Bool	alias of marshmallow.fields.Boolean
Boolean(*, truthy, falsy, **kwargs)	A boolean field.
Constant(constant, **kwargs)	A field that (de)serializes to a preset constant.
Date(format, **kwargs)	ISO8601-formatted date string.
DateTime(format, **kwargs)	A formatted datetime string.
Decimal(places, rounding, *, allow_nan, …)	A field that (de)serializes to the Python decimal.Decimal type.
Dict(keys, type]] = None, values, …)	A dict field.
Email(*args, **kwargs)	A validated email field.
Field(*, default, missing, data_key, …)	Basic field from which other fields should extend.
Float(*, allow_nan, as_string, **kwargs)	A double as an IEEE-754 double precision string.
Function(serialize, Any], Callable[[Any, …)	A field that takes the value returned by a function.
IP(*args[, exploded])	A IP address field.
IPInterface(*args[, exploded])	A IPInterface field.
IPv4(*args[, exploded])	A IPv4 address field.
IPv4Interface(*args[, exploded])	A IPv4 Network Interface field.
IPv6(*args[, exploded])	A IPv6 address field.
IPv6Interface(*args[, exploded])	A IPv6 Network Interface field.
Int	alias of marshmallow.fields.Integer
Integer(*, strict, **kwargs)	An integer field.
List(cls_or_instance, type], **kwargs)	A list field, composed with another Field class or instance.
Mapping(keys, type]] = None, values, …)	An abstract class for objects with key-value pairs.
Method(serialize, deserialize, **kwargs)	A field that takes the value returned by a Schema method.
NaiveDateTime(format, *, timezone, **kwargs)	A formatted naive datetime string.
Nested(nested, type, str, Callable[[], …)	Allows you to nest a Schema inside a field.
Number(*, as_string, **kwargs)	Base class for number fields.
Pluck(nested, type, str, Callable[[], …)	Allows you to replace nested data with one of the data’s fields.
Raw(*, default, missing, data_key, …)	Field that applies no formatting.
Str	alias of marshmallow.fields.String
String(*, default, missing, data_key, …)	A string field.
Time(format, **kwargs)	A formatted time string.
TimeDelta(precision, **kwargs)	A field that (de)serializes a datetime.timedelta object to an integer and vice versa.
Tuple(tuple_fields, *args, **kwargs)	A tuple field, composed of a fixed number of other Field classes or instances
URL	alias of marshmallow.fields.Url
UUID(*, default, missing, data_key, …)	A UUID field.
Url(*, relative, schemes, Set[str]]] = None, …)	A validated URL field.

通过可选参数使用它的更多功能

only: 返回过滤后的输出，只返回only指定的字段

summary_schema = UserSchema(only=("name", "email"))
summary_schema.dump(user)
# {"name": "Monty", "email": "monty@python.org"}

many: 处理可迭代对象

user1 = User(name="Mick", email="mick@stones.com")
user2 = User(name="Keith", email="keith@stones.com")
users = [user1, user2]
schema = UserSchema(many=True)
result = schema.dump(users)  # OR UserSchema().dump(users, many=True)
pprint(result)
# [{'name': u'Mick',
#   'email': u'mick@stones.com',
#   'created_at': '2014-08-17T14:58:57.600623+00:00'}
#  {'name': u'Keith',
#   'email': u'keith@stones.com',
#   'created_at': '2014-08-17T14:58:57.600623+00:00'}]

required: 必须字段

partial: 忽视必须字段

class UserSchema(Schema):
    name = fields.String(required=True)
    age = fields.Integer(required=True)

result = UserSchema().load({"age": 42}， partial=("name",))# partial=True：忽视全部必须字段
print(result)  # => {'age': 42}

missing: 指定默认反序列化缺失的值
default : 指定默认序列化缺失的值

class UserSchema(Schema):
    id = fields.UUID(missing=uuid.uuid1)
    birthdate = fields.DateTime(default=dt.datetime(2017, 9, 29))

UserSchema().load({})
# {'id': UUID('337d946c-32cd-11e8-b475-0022192ed31b')}
UserSchema().dump({})
# {'birthdate': '2017-09-29T00:00:00+00:00'}