fix(types): allow running from Python 3.7

[henryiii]

No description provided.

[sourcery-ai]

Sourcery Code Quality Report

Merging this PR leaves code quality unchanged.

Quality metrics	Before	After	Change
Complexity	0.61 ⭐	0.61 ⭐	0.00
Method Length	82.38 🙂	82.38 🙂	0.00
Working memory	8.11 🙂	8.11 🙂	0.00
Quality	72.59% 🙂	72.59% 🙂	0.00%

Other metrics	Before	After	Change
Lines	142	142	0

Changed files	Quality Before	Quality After	Quality Change
tests/test_accumulators.py	72.59% 🙂	72.59% 🙂	0.00%

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
tests/test_accumulators.py	test_sum_weighed_mean	0 ⭐	162 😞	10 😞	61.70% 🙂	Try splitting into smaller methods. Extract out complex expressions
tests/test_accumulators.py	test_sum_mean	0 ⭐	114 🙂	10 😞	67.14% 🙂	Extract out complex expressions

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The 👍 and 👎 indicate whether the quality has improved or gotten worse with this pull request.

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