Pydantic 是一個(gè)使用Python類型注解進(jìn)行數(shù)據(jù)驗(yàn)證和管理的模塊。安裝方法非常簡(jiǎn)單，打開終端輸入：

pip install pydantic

它類似于 Django DRF 序列化器的數(shù)據(jù)校驗(yàn)功能，不同的是，Django里的序列化器的Field是有限制的，如果你想要使用自己的Field還需要繼承并重寫它的基類：

# Django 序列化器的一個(gè)使用例子，你可以和下面Pydantic的使用作對(duì)比
class Book(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=32)
    price = models.DecimalField(max_digits=5, decimal_places=2)
    author = models.CharField(max_length=32)
    publish = models.CharField(max_length=32)

而 Pydantic 基于Python3.7以上的類型注解特性，實(shí)現(xiàn)了可以對(duì)任何類做數(shù)據(jù)校驗(yàn)的功能：

上滑查看更多代碼

# Pydantic 數(shù)據(jù)校驗(yàn)功能
from datetimeimport datetime
from typingimport List, Optional
from pydanticimport BaseModel


class User(BaseModel):
    id: int
name ='John Doe'
    signup_ts: Optional[datetime] =None
    friends: List[int] = []


external_data = {
'id':'123',
'signup_ts':'2019-06-01 12:22',
'friends': [1,2,'3'],
}
user = User(**external_data)
print(user.id)
print(type(user.id))
# > 123
# > < class 'int' >
print(repr(user.signup_ts))
# > datetime.datetime(2019, 6, 1, 12, 22)
print(user.friends)
# > [1, 2, 3]
print(user.dict())
"""
{
    'id': 123,
    'signup_ts': datetime.datetime(2019, 6, 1, 12, 22),
    'friends': [1, 2, 3],
    'name': 'John Doe',
}
"""

從上面的基本使用可以看到，它甚至能自動(dòng)幫你做數(shù)據(jù)類型的轉(zhuǎn)換，比如代碼中的 user.id, 在字典中是字符串，但經(jīng)過Pydantic校驗(yàn)器后，它自動(dòng)變成了int型，因?yàn)閁ser類里的注解就是int型。

當(dāng)我們的數(shù)據(jù)和定義的注解類型不一致時(shí)會(huì)報(bào)這樣的Error：

from datetime import datetime
from typing import List, Optional
from pydantic import BaseModel


class User(BaseModel):
    id: int
    name = 'John Doe'
    signup_ts: Optional[datetime] = None
    friends: List[int] = []


external_data = {
    'id': '123',
    'signup_ts': '2019-06-01 12:222',
    'friends': [1, 2, '3'],
}
user = User(**external_data)
"""
Traceback (most recent call last):
  File "1.py", line 18, in < module >
    user = User(**external_data)
  File "pydanticmain.py", line 331, in pydantic.main.BaseModel.__init__
pydantic.error_wrappers.ValidationError: 1 validation error for User
signup_ts
  invalid datetime format (type=value_error.datetime)
"""

即 "invalid datetime format", 因?yàn)槲覀魅氲?signup_ts 不是標(biāo)準(zhǔn)的時(shí)間格式（多了個(gè)2）。

1. Pydantic模型數(shù)據(jù)導(dǎo)出 ****

通過Pydantic模型中自帶的 json 屬性方法，能讓經(jīng)過校驗(yàn)后的數(shù)據(jù)一行命令直接轉(zhuǎn)成 json 字符串，如前文中的 user 對(duì)象：

print(user.dict()) # 轉(zhuǎn)為字典
"""
{
    'id': 123,
    'signup_ts': datetime.datetime(2019, 6, 1, 12, 22),
    'friends': [1, 2, 3],
    'name': 'John Doe',
}
"""
print(user.json()) # 轉(zhuǎn)為json
"""
{"id": 123, "signup_ts": "2019-06-01T12:22:00", "friends": [1, 2, 3], "name": "John Doe"}
"""

非常方便。它還支持將整個(gè)數(shù)據(jù)結(jié)構(gòu)導(dǎo)出為 schema json，它能完整地描述整個(gè)對(duì)象的數(shù)據(jù)結(jié)構(gòu)類型：

上滑查看更多代碼

print(user.schema_json(indent=2))
"""
{
  "title": "User",
  "type": "object",
  "properties": {
    "id": {
      "title": "Id",
      "type": "integer"
    },
    "signup_ts": {
      "title": "Signup Ts",
      "type": "string",
      "format": "date-time"
    },
    "friends": {
      "title": "Friends",
      "default": [],
      "type": "array",
      "items": {
        "type": "integer"
      }
    },
    "name": {
      "title": "Name",
      "default": "John Doe",
      "type": "string"
    }
  },
  "required": [
    "id"
  ]
}
"""

2.數(shù)據(jù)導(dǎo)入

除了直接定義數(shù)據(jù)校驗(yàn)?zāi)Ｐ停€能通過ORM、字符串、文件導(dǎo)入到數(shù)據(jù)校驗(yàn)?zāi)Ｐ停?/p>

比如字符串（raw）：

from datetime import datetime
from pydantic import BaseModel


class User(BaseModel):
    id: int
    name = 'John Doe'
    signup_ts: datetime = None
      
m = User.parse_raw('{"id": 123, "name": "James"}')
print(m)
# > id=123 signup_ts=None name='James'

此外，它能直接將ORM的對(duì)象輸入，轉(zhuǎn)為Pydantic的對(duì)象，比如從Sqlalchemy ORM：

上滑查看更多代碼

from typingimport List
from sqlalchemyimport Column, Integer, String
from sqlalchemy.dialects.postgresqlimport ARRAY
from sqlalchemy.ext.declarativeimport declarative_base
from pydanticimport BaseModel, constr

Base = declarative_base()


class CompanyOrm(Base):
    __tablename__ ='companies'
    id = Column(Integer, primary_key=True, nullable=False)
    public_key = Column(String(20), index=True, nullable=False, unique=True)
name = Column(String(63), unique=True)
    domains = Column(ARRAY(String(255)))


class CompanyModel(BaseModel):
    id: int
    public_key: constr(max_length=20)
name: constr(max_length=63)
    domains: List[constr(max_length=255)]

class Config:
        orm_mode =True


co_orm = CompanyOrm(
    id=123,
    public_key='foobar',
name='Testing',
    domains=['example.com','foobar.com'],
)
print(co_orm)
# > < models_orm_mode.CompanyOrm object at 0x7f0bdac44850 >
co_model = CompanyModel.from_orm(co_orm)
print(co_model)
# > id=123 public_key='foobar' name='Testing' domains=['example.com',
# > 'foobar.com']

從Json文件導(dǎo)入：

from datetime import datetime
from pathlib import Path
from pydantic import BaseModel


class User(BaseModel):
    id: int
    name = 'John Doe'
    signup_ts: datetime = None
      
path = Path('data.json')
path.write_text('{"id": 123, "name": "James"}')
m = User.parse_file(path)
print(m)

從pickle導(dǎo)入：

import pickle
from datetime import datetime
from pydantic import BaseModel

pickle_data = pickle.dumps({
    'id': 123,
    'name': 'James',
    'signup_ts': datetime(2017, 7, 14)
})
m = User.parse_raw(
    pickle_data, content_type='application/pickle', allow_pickle=True
)
print(m)
# > id=123 signup_ts=datetime.datetime(2017, 7, 14, 0, 0) name='James'

3.自定義數(shù)據(jù)校驗(yàn)

你還能給它增加 validator 裝飾器，增加你需要的校驗(yàn)邏輯：

上滑查看更多代碼

from sklearn.metrics import confusion_matrix
from sklearn.linear_model import LogisticRegression
from sklearn.preprocessing import StandardScaler
from sklearn.model_selection import train_test_split
from sklearn.preprocessing import LabelEncoder
import numpy as np
import matplotlib.pyplot as plt
import pandas as pd

# 1.導(dǎo)入數(shù)據(jù)集
dataset = pd.read_csv('Social_Network_Ads.csv')
X = dataset.iloc[:, [1, 2, 3]].values
Y = dataset.iloc[:, 4].values

# 性別轉(zhuǎn)化為數(shù)字
labelencoder_X = LabelEncoder()
X[:, 0] = labelencoder_X.fit_transform(X[:, 0])

# 2.將數(shù)據(jù)集分成訓(xùn)練集和測(cè)試集
X_train, X_test, y_train, y_test = train_test_split(
    X, Y, test_size=0.25, random_state=0)

# 3.特征縮放
sc = StandardScaler()
X_train = sc.fit_transform(X_train)
X_test = sc.transform(X_test)

# 4.訓(xùn)練
classifier = LogisticRegression()
classifier.fit(X_train, y_train)

# 5.預(yù)測(cè)
y_pred = classifier.predict(X_test)

# 6.評(píng)估預(yù)測(cè)

# 生成混淆矩陣
from sklearn.metrics import confusion_matrix
cm = confusion_matrix(y_test, y_pred)
print(cm)

上面，我們?cè)黾恿巳N自定義校驗(yàn)邏輯：

1.name 必須帶有空格

2.password2 必須和 password1 相同

3.username 必須為字母

讓我們?cè)囋囘@三個(gè)校驗(yàn)是否有效：

user = UserModel(
    name='samuel colvin',
    username='scolvin',
    password1='zxcvbn',
    password2='zxcvbn',
)
print(user)
# > name='Samuel Colvin' username='scolvin' password1='zxcvbn' password2='zxcvbn'

try:
    UserModel(
        name='samuel',
        username='scolvin',
        password1='zxcvbn',
        password2='zxcvbn2',
    )
except ValidationError as e:
    print(e)
    """
    2 validation errors for UserModel
    name
      must contain a space (type=value_error)
    password2
      passwords do not match (type=value_error)
    """

可以看到，第一個(gè)UserModel里的數(shù)據(jù)完全沒有問題，通過校驗(yàn)。

第二個(gè)UserModel里的數(shù)據(jù)，由于name存在空格，password2和password1不一致，無法通過校驗(yàn)。因此我們定義的自定義校驗(yàn)器完全有效。

4.性能表現(xiàn)

這是最令我驚訝的部分，Pydantic 比 Django-rest-framework 的校驗(yàn)器還快了12.3倍：