Peter Lovett is a programmer and trainer.
Python’s dark corners. Covering 2.x with a few tips on 3; things to avoid, etc. Python is a fantastic language but it’s not perfect and there are a few dark corners which need to be worked around.
Python is a deceptively simple language: the surface simplicity hides a deal of complexity.
Reference to the algorithmic trading incident.
OO
Python really is object oriented. This has a few more implications: “modules” and functions are first-class.
References
Python uses references by default. Use is for reference equality, not ==.
Some types (int, tuple, etc) are immutable.
Rebinding is sometimes an accident. When of a built-in, it’s often
catastrophic. Use __builtin__ to get these things back.
Pass by reference is the default (and only option). The only pass by value is
to copy it. Lots of options for lists (slice [:]), the copy module.
Operators
No ++ or -- operators. “Mutating” operators are designed so as not to be
mutating: +=, etc. rather than ++.
Typing
If you’re checking types, you’re doing it wrong. “Duck typing”. #sigh
Numerics
Floating point arithmetic is floating point arithmetic.
Tuples
Immutable, but only the tuple itself (i.e. the references it contains, not their referents).
Arguments
Support both ordinal and keyword parameters.
Default values. Default values are created at load time, so should probably be immutable.
Namespaces
Scoping: scoping of variables is based on use within the scope, not dynamic.
Visibility of globals. Better to just avoid variables in global scope.