Yes, Python dictionaries are ordered starting from Python 3.7 and later. The order of the items in a dictionary is guaranteed to be the same as the order in which they were inserted. This behavior became part of the official Python language specification in version 3.7, although it was already an implementation detail in CPython 3.6.
Python Dictionaries in Versions Before 3.7
Unordered Behavior in Python 3.5 and Earlier
Before Python 3.7, dictionaries did not guarantee any order. The items in a dictionary were unordered, and the iteration over the dictionary would return items in an arbitrary order, which could change between runs of the program.
- Python 3.5 and earlier: No guarantee of insertion order.
- Example (Python 3.5 or earlier):
#python
my_dict = {'a': 1, 'b': 2, 'c': 3}
for key, value in my_dict.items():
print(key, value)
Output could vary, for example:
#css
c 3
b 2
a 1
Guaranteed Insertion Order
Starting with Python 3.7, dictionaries now guarantee that the order of items reflects the order in which they were inserted into the dictionary. This change provides more predictable behavior when iterating over a dictionary.
- Insertion Order is Preserved: Items are iterated in the same order they were added.
- Key Takeaway: You can now rely on the order of keys and values in a dictionary.
Ordered Behavior in Python 3.7+
Here’s an example demonstrating the behavior in Python 3.7 and later:
#python
# Python 3.7+ (Guaranteed ordered behavior)
my_dict = {'a': 1, 'b': 2, 'c': 3}
for key, value in my_dict.items():
print(key, value)
Output:
#css
a 1
b 2
c 3
In this case, the dictionary maintains the order of insertion, and the items are printed in the same order they were added to my_dict.
Key Considerations
Insertion Order vs. Sorting Order
It’s important to note that the insertion order is what is preserved, not any sorting order of the keys. If you want to sort the keys, you would need to do so explicitly using functions like sorted().
#python
# Sorting keys alphabetically
sorted_keys = sorted(my_dict.keys())
for key in sorted_keys:
print(key, my_dict[key])
Note:
In Python 3.7 and later, dictionaries are ordered, meaning the order of key-value pairs is preserved as they are inserted. This provides more predictable behavior, making it easier to work with data structures where the order of items matters. However, it’s essential to remember that this is based on insertion order, not any automatic sorting of keys.
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