抽象基类一般用于规定子类必须重新定义某些方法。比如 web 框架中的 cache 部分的基类一般类似下面这样:
class BaseCache(object):
def get(self, key):
raise NotImplementedError('subclasses of BaseCache must provide a get() method')
def set(self, key, value, timeout=60):
raise NotImplementedError('subclasses of BaseCache must provide a set() method')
class MemcachedCache(BaseCache):
def get(self, key):
value = self._cache ...sudo apt-get install postgresql-client sudo apt-get install postgresql
sudo service postgresql start
sudo -u postgres psql
或
psql -U dbuser -d exampledb -h 127.0.0.1 -p 5432
退出
postgres=# \q
sudo -u postgres createuser dbuser
或
sudo -u postgres psql postgres ...
两个模块间互相导入时，可能会出现如下的问题：
# a.py
from b import y
print y
x = 5
# b.py
from a import x
print x
y = 10
>>> import b
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "b.py", line 1, in <module>
from a import x
File "a.py", line ...