Avoiding the "RuntimeError: dictionary changed size during iteration" Error
Attempting to modify a dictionary while iterating over it, as seen in the code snippet below, can trigger the "RuntimeError: dictionary changed size during iteration" error:
<code class="python">d = {'a': [1], 'b': [1, 2], 'c': [], 'd':[]} for i in d: if not d[i]: d.pop(i)</code>
To overcome this limitation, various approaches can be employed:
Python 2.x and 3.x:
Force a copy of the keys using 'list':
<code class="python">for i in list(d):</code>
Python 3.x (and later):
Use 'collections.OrderedDict':
<code class="python">from collections import OrderedDict for i in OrderedDict(d):</code>
Alternative Solutions:
<code class="python">new_d = {} for key, value in d.items(): if value: new_d[key] = value</code>
<code class="python">keys_to_pop = list(d) for i in keys_to_pop: if not d[i]: d.popitem(i)</code>
By leveraging these techniques, you can circumvent the "RuntimeError: dictionary changed size during iteration" error when handling dictionaries in Python.
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