In Python 2.7 prior to 2.7.3, or Python 3 prior to 3.3, iterating a dictionary would -- if it always contained the same set of keys -- be in a consistent order across multiple runs of the same program. This was an implementation detail not to be relied on.

Starting in 2.7.3 and 3.3, the hashing algorithm applied a per-process random salt to certain built-in types, in order to mitigate a potential denial-of-service vector by crafting dictionary keys which cause hash collisions. Unless the PYTHONHASHSEED environment variable was set to a consistent value, iteration over a dictionary was no longer accidentally consistent across runs.

In 3.6, the dictionary implementation was rewritten to drastically improve performance. As a side effect, dictionary iteration became consistent again, this time determined by insertion order. In 3.6, this consistency was an implementation detail and not to be relied on.

Beginning with 3.7, dictionary iteration order is finally guaranteed by the language, independent of implementation, and goes by insertion order.

CPython interates in this fashion since 3.6, but it is not part of the Python spec.

Might be a bit contentious but it's not supposed to be relied upon