What rules does Pandas use to generate a view vs a copy?
Here's the rules, subsequent override:
All operations generate a copy
If
inplace=Trueis provided, it will modify in-place; only some operations support thisAn indexer that sets, e.g.
.loc/.iloc/.iat/.atwill set inplace.An indexer that gets on a single-dtyped object is almost always a view (depending on the memory layout it may not be that's why this is not reliable). This is mainly for efficiency. (the example from above is for
.query; this will always return a copy as its evaluated bynumexpr)An indexer that gets on a multiple-dtyped object is always a copy.
Your example of chained indexing
df[df.C <= df.B].loc[:,'B':'E']is not guaranteed to work (and thus you shoulld never do this).
Instead do:
df.loc[df.C <= df.B, 'B':'E']as this is faster and will always work
The chained indexing is 2 separate python operations and thus cannot be reliably intercepted by pandas (you will oftentimes get a SettingWithCopyWarning, but that is not 100% detectable either). The dev docs, which you pointed, offer a much more full explanation.