Generatore pymongo fallisce - 'ritorno' con generatore di tesi all'interno

Question

Sto cercando di fare quanto segue:

def get_collection_iterator(collection_name, find={}, criteria=None):
    collection = db[collection_name]
    # prepare the list of values of collection
    if collection is None:
        logging.error('Mongo could not return the collecton - ' + collection_name)
        return None

    collection = collection.find(find, criteria)
    for doc in collection:
        yield doc 

e chiamando come:

def get_collection():
    criteria = {'unique_key': 0, '_id': 0}
    for document in Mongo.get_collection_iterator('contract', {}, criteria):
        print document 

e vedo l'errore che dice:

File "/Users/Dev/Documents/work/dw/src/utilities/Mongo.py", line 96
    yield doc
SyntaxError: 'return' with argument inside generator 

che cosa è che sto facendo errato qui?

Answer 1

Sembra che il problema è che Python non permette di mixare return e yield -. Si utilizza sia all'interno get_collection_iterator

Chiarimento (grazie a Rob mayoff): return x e yield non può essere mescolato, ma una nuda return possono

Answer 2

Your problem is in the event None must be returned, but it is detected as a syntax error since the return would break the iteration loop.

Generators that are intended to use yield to handoff values in loops can't use return with argument values, as this would trigger a StopIteration error. Rather than returning None, you may want to raise an exception and catch it in the calling context.

http://www.answermysearches.com/python-fixing-syntaxerror-return-with-argument-inside-generator/354/

def get_collection_iterator(collection_name, find={}, criteria=None):
    collection = db[collection_name]
    # prepare the list of values of collection
    if collection is None:
        err_msg = 'Mongo could not return the collecton - ' + collection_name
        logging.error(err_msg)
        raise Exception(err_msg)

    collection = collection.find(find, criteria)
    for doc in collection:
        yield doc 

You could make a special exception for this too if need be.