Fix some SyntaxWarnings

[Ferenc-]

• On Python 3.8.5 during normal execution the following is logged:
  SyntaxWarning: "is" with a literal. Did you mean "=="?

🚨Please review the guidelines for contributing to this repository.

Proposed changes

Eliminate some annoying SyntaxWarning messages.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have read the CONTRIBUTING doc
• I agree to contribute my changes under the project's LICENSE
• I have checked that the unit tests pass locally with my changes
• I have checked the style of the new code (lint/pep).
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

This should not change the functionality.

Reviewers

@felker @balta2ar

[Ferenc-]

The CI failures seem to be non-relevant:

No matching distribution found for urllib3>=1.23 (from -r requirements.txt (line 4))
Command exited with code 1

Is there a way to re-trigger it?

[coveralls]

Coverage increased (+0.2%) to 73.594% when pulling 1e058b3 on Ferenc-:SYNTAX_FIX into f9a9a26 on coursera-dl:master.

[coveralls]

Coverage increased (+0.2%) to 73.594% when pulling 1e058b3 on Ferenc-:SYNTAX_FIX into f9a9a26 on coursera-dl:master.

[Ferenc-]

@felker could you take a look at this?