chore: format code with black and isort.

[overcat]

No description provided.

[codecov]

Codecov Report

Merging #506 (40732fe) into dev (359d97c) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #506      +/-   ##
==========================================
- Coverage   99.03%   99.03%   -0.01%     
==========================================
  Files         129      129              
  Lines        8892     8878      -14     
==========================================
- Hits         8806     8792      -14     
  Misses         86       86              

Flag	Coverage Δ
unittests	99.03% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
stellar_sdk/exceptions.py	90.47% <ø> (ø)
stellar_sdk/keypair.py	98.92% <ø> (ø)
tests/sep/test_account_memo_requirements.py	100.00% <ø> (ø)
tests/sep/test_txrep.py	100.00% <ø> (ø)
tests/test_fee_bump_transaction.py	100.00% <ø> (ø)
tests/test_transaction_builder.py	100.00% <ø> (ø)
stellar_sdk/__init__.py	100.00% <100.00%> (ø)
stellar_sdk/account.py	94.28% <100.00%> (ø)
stellar_sdk/asset.py	100.00% <100.00%> (ø)
stellar_sdk/base_transaction_envelope.py	100.00% <100.00%> (ø)
... and 76 more

[overcat]

python/typed_ast#111