I'm struggling with implementing the Bridge design pattern (or an alternative such as Adapter) in Python
I want to be able to write code like this to dump database schemas based on a supplied URL:
urls = ['sqlite://c:\\temp\\test.db', 'oracle://user:password#tns_name'];
for url in urls:
db = Database(url);
schema = db.schema()
I've got classes defined as
class Database():
def __init__(self, url):
self.db_type = string.split(self.url, "://")[0]
class Oracle():
def schema(self):
# Code to return Oracle schema
class SQLite():
def schema(self):
# Code to return SQLite schema
How can I "glue" these 3 classes together so I can get the first code block to execute correctly? I've Googled around, but must be having a thick day as it's just not coming together in my mind...
Thanks in advance
Use a Factory pattern instead:
class Oracle(object):
...
class SQLite(object):
...
dbkind = dict(sqlite=SQLite, oracle=Oracle)
def Database(url):
db_type, rest = string.split(self.url, "://", 1)
return dbkind[db_type](rest)
Related
i am having a simple app example here:
say i have this piece of code which handles requests from user to get a list of books stored in a database.
from .handlers import all_books
#apps.route('/show/all', methods=['GET'])
#jwt_required
def show_books():
user_name = get_jwt_identity()['user_name']
all_books(user_name=user_name)
and in handlers.py i have :
def all_books(user_name):
db = get_db('books')
books = []
for book in db.books.find():
books.append(book)
return books
but while writing unit tests i realised if i use get_db() inside all_books() it would be harder to unit test the method.
so i thought this would be the good way.
from .handlers import all_books
#apps.route('/show/all', methods=['GET'])
#jwt_required
def show_books():
user_name = get_jwt_identity()['user_name']
db = get_db('books')
collection = db.books
all_books(collection=collection)
def all_books(collection):
books = []
for book in collection.find():
books.append(book)
return books
i want to know what is the good design to use?
have all code doing one thing at one place like the first example or the second example is good.
To me first one seems more clear as it has all related logic at one place. but its easier to pass a fake collection in second case to unit test it.
you should probably use the mock library see: https://docs.python.org/3/library/unittest.mock.html#quick-guide
(if you use python2 you will need pip install mock)
def test_it():
from unittest.mock import Mock,patch
with patch.object(get_db,'function',Mock(return_value=Mock(books=[1,2,3]))) as mocked_db:
x = get_db("ASDASD")
console.log(x.books)
# you can also do cool stuff like this
assert mocked_db.calledwith("ASDASD")
of coarse for yours you will have to construct a slightly more complex object
my_mocked_get_db = Mock(return_value=Mock(books=Mock(find=[1,2,3,4])))
with patch.object(get_db,'function',my_mocked_get_db) as mocked_db:
x = get_db("ASDASD")
print(x.books.find())
I want to write a method to parse a site with requests library, the method should take a part of url having base_url in it and perform the get request on this, the main problem is that I do not know how to make it better;
What I have in mind now is:
import requests
class Response:
# ...
def site_parser(self, atom):
base_url="https://example.com/"
def category1(self):
return requests.get(base_url + category1/ + atom).text
def category2(self):
return requests.get(base_url + category2/ + atom).text
if __name == "__main__":
def main():
result = Response()
result.site_parser.category1("atom")
result.site_parser.category2("atom")
so needed data has the same base url but different dirs to get into, and I need to gen each dir if only the method was called afterwards. is there a way of doing this properly? I wouuld like to avoid making base url global variable
It seems to me that what you need is another class.
class Response:
# ... Some dark magic here ...
def site_parser(self, atom):
return ResponseParser(self, atom)
class ResponseParser:
def __init__(self, res, atom):
self.atom = atom
self.res = res
self.base_url = "https://example.com/"
def category1(self):
# ... Do stuff ...
def category2(self):
# ... Do stuff ...
Then you call it with
result = Response()
result.site_parser("atom").category1()
If you really insist on getting rid of the parentheses on the site_parser call, you could move the "atom" bit to the categoryN methods and turn site_parser into a property, but IMO that would probably just confuse people more than anything.
As a functional programmer, I love nested functions and closures as much as the next guy, but it seems to me that, based on the limited example you've given, having a second helper class is probably going to be the more readable way to go about this in this case.
I make use of uwsgi, django and django-rest-framework to develop one application.
I introduced one class variable in renderer class, this variable will be fill as one part of response.
the problem seems likes as following:
class xxxRenderer(xxxBase)
response_pb_msg = obj # it's one instance of protobuf message
def render():
if True:
self.response_pb_msg.items = []
else:
self.response_pb_msg.retCode = 100
self.response_pb_msg.otherXXXX = xxxx
In django logger handler, I access this class variable again like following:
xxxRenderer.response_pb_msg.ParseFromString(body)
after the first response, this class variable 'response_pb_msg' only has one property "retCode"
but the second response, it has three properties "retCode", "otherXXXX " and "items "
it's strange, the second response contain all content which was exist in the first response.
after a time, I re-wrote this class like following:
class xxxBaserender(xxRender)
def __init__():
if self.response_pb_msg_cls is not None and isinstance(self.response_pb_msg_cls, GeneratedProtocolMessageType):
self.response_pb_message = self.response_pb_msg_cls()
class xxxRenderer(xxxBaserender)
response_pb_msg_cls = msgName # the class of protobuf message
theoretically, the second class is ok. I tested, didn't duplicate that question.
Let's return to where we started
Every request finisehd, all resoure should be clean.
but I'm very puzzled with that problem, it seems that class variable not been released in uwsgi progress after response return.
I read “PEP 3333”， didn't get any valuable information.
I think I didn't fully understand class variaable, wsgi and web processing flow in python.
anyone can help me to understand this problem?
thanks vey much.
I'm trying to create several URLs on my serv thanks to a loop . The issue is that each function I create in a app.route can't have the same name than the others . And I don't know how to create different function names ...
Here is the code :
json_tweets = []
for line in open('C:\Users\Benjamin\Desktop\DashboardProject\last_rated_set.json',"r"):
json_tweets.append(json.loads(line,"ISO-8859-1"))
cashtag_tab = []
for tweet in json_tweets:
if not(tweet['cashtag'] in cashtag_tab) :
cashtag_tab.append(tweet['cashtag'])
for i in range(0,(len(cashtag_tab)-1)) :
var=cashtag_tab[i]
#app.route("/"+var)
def company(var) :
finance=Share(var)
datas = finance.get_historical('2014-01-01', '2014-12-31')
datas = json.dumps(datas, default=json_util.default)
return datas
I'm getting the error AssertionError : View function mapping is overwritting an existing endpoint function : company
This fails because Flask derives the endpoint name from the function by default, but it would anyway fail later because the function company requires an argument var and the route is not parameterised. The simplest option would be just checking the value inside the handler:
#api.route('/<var>')
def company(var):
if var not in cashtag_tab:
abort(404)
If you want all the routes to be in the routing map for any reason, I once needed a similar thing and came up with something like this:
def url_family(source, methods=('GET',)):
def decorator(f):
for entry in source:
# create a handler that delegates to your function
def view_func(entry=entry, **kwargs):
return f(entry, **kwargs)
endpoint = '{0}_{1}'.format(f.__name__, entry)
url = '/{0}'.format(entry)
api.add_url_rule(url,
methods=methods,
endpoint=endpoint,
view_func=view_func)
return decorator
Then you register the handlers as:
#url_family(cashtag_tab)
def company(var):
...
Assuming that you are using flask now, you should consider Custom URL Converter. Check links below
http://flask.pocoo.org/docs/0.10/api/#flask.Flask.url_map - url_map UrlConverter API
https://exploreflask.com/views.html#url-converters - example url converter
https://stackoverflow.com/a/5872904/3451543 - RegexConverter by Philip Southam
Anyway, specifying more details on your question is always helpful to get accurate answer :)
I am using the cloudant python library to connect to my cloudant account.
Here is the code I have so far:
import cloudant
class WorkflowsCloudant(cloudant.Account):
def __init__(self):
super(WorkflowsCloudant, self).__init__(settings.COUCH_DB_ACCOUNT_NAME,
auth=(settings.COUCH_PUBLIC_KEY,
settings.COUCH_PRIVATE_KEY))
#blueprint.route('/<workflow_id>')
def get_single_workflow(account_id, workflow_id):
account = WorkflowsCloudant()
db = account.database(settings.COUCH_DB_NAME)
doc = db.document(workflow_id)
resp = doc.get().json()
if resp['account_id'] != account_id:
return error_helpers.forbidden('Invalid Account')
return jsonify(resp)
This Flask controller will have CRUD operations inside of it, but with the current implementation, I will have to set the account and db variables in each method before performing operations on the document I want to view/manipulate. How can I clean up (or DRY up) my code so that I only have to call to my main WorkflowsCloudant class?
I don't know cloudant, so I may be totally off base, but I believe this answers your question:
Delete the account, db, and doc lines from get_single_workflow.
Add the following lines to __init__:
db = account.database(settings.COUCH_DB_NAME)
self.doc = db.document(workflow_id)
Change the resp line in get_single_workflow to:
resp = WorkflowsCloudant().doc.get().json()