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    <p>From what I understand you are doings something like the following:</p> <pre><code>for i in range(0,100): ent = My_Entity() # create and save entity db.put(ent) ent = db.get(ent.key()) # get, modify and save the entity ent.property = 'foo' db.put(ent) ent.get(ent.key()) # get and delete the entity db.delete(my_ent) </code></pre> <p>with some error checking to make sure you have entities to delete, modify, and you are running into a bunch of errors about finding the entity to delete or modify. As you say, this is because the calls aren't guaranteed to be executed in order.</p> <blockquote> <p>However, I want to understand how to handle these kind of situation where concurrent operation is being done with a Entity.</p> </blockquote> <p>You're best bet for this is to batch any modifications you are doing for an entity persisting. For example if you are going to be creating/saving/modifying/savings or modifying/saving/deleting where ever possible try to combine these steps (ie create/modify/save or modify/delete). Not only will this avoid the errors you're seeing but it will also cut down on your RPCs. Following this strategy the above loop would be reduced to... </p> <pre><code>prop = None for i in range(0,100): prop = 'foo' </code></pre> <p>Put in other words, for anything that requires setting/deleting that quickly just use a local variable. That's GAE's answer for you. After you figure out all the quick stuff you can't persist that information in an entity.</p> <p>Other than that there isn't much you can do. <a href="https://developers.google.com/appengine/docs/python/datastore/transactions" rel="nofollow">Transactions</a> can help you if you need to make sure a bunch of entities are updated together but won't help if you're trying to multiple things to one entity at once.</p> <p>EDIT: You could also look at the <a href="http://code.google.com/p/appengine-pipeline/" rel="nofollow">pipelines API</a>.</p>
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    1. CORight, batch transaction would be suitable for create/modify/save, there's another issue I want to tackle, that is, when two threads try to update a Entity (let say a points value) at the same time, that means when both threads save, the value is not the expected value, say for a increment points function
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    2. COAs a work-around you could go with the method that Brett Slatkin suggests on his Google IO talk [Building high-throughput data pipelines with Google App Engine](http://www.google.com/events/io/2010/sessions/high-throughput-data-pipelines-appengine.html) 33:00
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