Improve code for USMetadata

[avdata99]

The code in the USMetadata extension requires to be improved following flake8 analysis

How to reproduce

Run flake8 . --count --ignore E501 --show-source --statistics

2     E101 indentation contains mixed spaces and tabs
3     E124 closing bracket does not match visual indentation
3     E127 continuation line over-indented for visual indent
28    E128 continuation line under-indented for visual indent
1     E129 visually indented line with same indent as next logical line
1     E201 whitespace after '{'
2     E225 missing whitespace around operator
8     E231 missing whitespace after ','
13    E251 unexpected spaces around keyword / parameter equals
1     E261 at least two spaces before inline comment
5     E265 block comment should start with '# '
1     E301 expected 1 blank line, found 0
3     E302 expected 2 blank lines, found 1
1     E303 too many blank lines (2)
1     E402 module-level import not at top of file
10    F401 'sqlalchemy.MetaData' imported but unused
2     F402 import 'v' from line 8 shadowed by loop variable
1     F841 local variable 'q' is assigned to but never used
18    W191 indentation contains tabs
2     W292 no newline at end of file
2     W603 '<>' is deprecated, use '!='
108

Expected behavior

Get zero errors

Actual behavior

Get 108 errors

[adborden]

Looks good.