Gotcha: Python dict iteration order is insertion order (but don't rely on it for semantics)

Python 3.7+ guarantees dict insertion order, but developers sometimes use dicts where ordered data structures (list of tuples, OrderedDict) would be more semantically correct.

Dict order is guaranteed but semantic intent matters:

# Insertion order IS guaranteed (Python 3.7+):
d = {'c': 3, 'a': 1, 'b': 2}
list(d.keys()) # ['c', 'a', 'b'] - guaranteed

# BUT: equality ignores order:
{'a': 1, 'b': 2} == {'b': 2, 'a': 1} # True!

# Use OrderedDict when order is SEMANTICALLY important:
from collections import OrderedDict
o1 = OrderedDict([('a', 1), ('b', 2)])
o2 = OrderedDict([('b', 2), ('a', 1)])
o1 == o2 # False! Order matters for equality

# When to use what:
# dict: Key-value lookup, order is incidental
# OrderedDict: Order is part of the data's meaning
# list of tuples: Ordered pairs, possibly with duplicate keys

# JSON gotcha: JSON objects have no guaranteed order
# Even though Python dicts are ordered, JSON parsers may not preserve order
import json
json.loads('{"b": 2, "a": 1}') # Order depends on parser

# Sorting a dict:
sorted_d = dict(sorted(d.items())) # By key
sorted_d = dict(sorted(d.items(), key=lambda x: x[1])) # By value

CPython 3.7+ guarantees insertion order as a language spec. But equality comparison ignores order, which can be surprising.