Maintenance of the code

[hoxbro]

This PR has done a couple of things to update the code:

1. Convert (most) of the format strings to f-strings.
   • This is done automatically with flynt for 3416921 and small manually changes in 4711233 and f2ce53e.
2. Remove bare except: in bcd6cda.
   • This is either done with except Exception: or except ImportError.
3. Remove checks if pandas are installed in c4a94a2, as it is a required dependency.
4. Remove Python 2 code in 6dc7315 and 74201a9
5. Cleanup bokeh imports in 223eea1.
   • MercatorTileSource, cartesian_to_axial, built_in_themes was in Bokeh 1.4.0

I noticed that file ...interface does not exist, so I think the following lines should be updated or removed if no longer needed.

holoviews/holoviews/plotting/bokeh/__init__.py

Lines 19 to 22 in e5224c6

	try:
	from ...interface import DFrame
	except:
	DFrame = None

[codecov-commenter]

Codecov Report

Merging #5509 (3fb9eba) into master (7d18655) will increase coverage by 0.09%.
The diff coverage is 63.35%.

@@            Coverage Diff             @@
##           master    #5509      +/-   ##
==========================================
+ Coverage   88.13%   88.22%   +0.09%     
==========================================
  Files         302      302              
  Lines       62357    62180     -177     
==========================================
- Hits        54959    54860      -99     
+ Misses       7398     7320      -78     

Impacted Files	Coverage Δ
holoviews/__init__.py	67.85% <0.00%> (ø)
holoviews/core/data/dask.py	90.00% <ø> (-0.18%)	⬇️
holoviews/core/data/multipath.py	86.55% <0.00%> (ø)
holoviews/core/data/util.py	58.92% <0.00%> (ø)
holoviews/core/decollate.py	95.93% <0.00%> (ø)
holoviews/core/traversal.py	62.50% <ø> (-1.64%)	⬇️
holoviews/element/annotation.py	87.28% <0.00%> (ø)
holoviews/element/path.py	86.87% <0.00%> (ø)
holoviews/element/sankey.py	95.04% <0.00%> (ø)
holoviews/element/stats.py	85.54% <0.00%> (ø)
... and 164 more

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[philippjfr]

I noticed that file ...interface does not exist, so I think the following lines should be updated or removed if no longer needed.

Yes please remove, it no longer exists. Since we now require Python >= 3.7 we could also consider swapping OrderedDict for regular dicts but that can be a separate PR.

[philippjfr]

I see that DFrame import was already removed so this looks good to me. Really appreciate this, thanks!