Dictionaries and Threads

[Aahz Maruch]

In article <3926A8EF.C3C1914B at jslove.net>, Jay Love  <jsliv at jslove.net> wrote:
>
>Are dictionary lookups threadsafe?
>
>ie, can I lookup and retrieve an item in a dictionary while another
>thread is adding an item?

In general yes, if you do it in single lines of code:

Thread1:
  var = dict['foo']

Thread2:
  dict['foo'] = 'bar'

However, if you have something like this

if dict.has_key('foo'):
  var = dict['foo']
else
  var = None

it is *not* thread-safe and you need to use some kind of locking
mechanism.  Of course, in this specific instance, you can replace the
above code with a single line:

var = dict.get('foo',None)


Note very carefully, though, that map() and reduce() are not
thread-safe.
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