[IBCDPE-220] fix lgtm.com code scanning warnings/recommendations

[thomasyu888]

LGTM.com is a website that does application security by doing code scanning with codeql and other tools to do code analysis. It produces "high" security vulnerabilities along with warnings and recommendations. It also has a feature that automatically reviews PRs for these concerns so that the code contributed doesn't contain issues.

• Specify empty dataframe with column headers to improve codebase
• Remove unused imports
• Do not set variables that aren't used
• Ignore some LGTM.com recommendations

[lgtm-com[bot]]

This pull request fixes 13 alerts when merging 7b9946889fdbdb3520e4f40518f0cb6e1e3b0077 into 168b1ec3b14fb8158a568aceefec91d0691590e9 - view on LGTM.com

fixed alerts:

• 6 for Unused import
• 4 for Unused local variable
• 1 for Implicit string concatenation in a list
• 1 for Module is imported with 'import' and 'import from'
• 1 for Variable defined multiple times

[lgtm-com[bot]]

This pull request fixes 13 alerts when merging 25a6a59162a5f9dbf5df4db2dd77a147b64926c9 into af9025c9fdbe33249b4e9fc1e749c5888d3c2336 - view on LGTM.com

fixed alerts:

• 6 for Unused import
• 4 for Unused local variable
• 1 for Implicit string concatenation in a list
• 1 for Module is imported with 'import' and 'import from'
• 1 for Variable defined multiple times

[lgtm-com[bot]]

This pull request fixes 13 alerts when merging 73e8e84abd257a003ac209dae59167050893dca9 into af9025c9fdbe33249b4e9fc1e749c5888d3c2336 - view on LGTM.com

fixed alerts:

• 6 for Unused import
• 4 for Unused local variable
• 1 for Implicit string concatenation in a list
• 1 for Module is imported with 'import' and 'import from'
• 1 for Variable defined multiple times