5.1.3 Function Call

The sort of symbolic programs generally written in Common Lisp often favor recursion over iteration, or have inner loops so complex that they involve multiple function calls. Such programs spend a larger fraction of their time doing function calls than is the norm in other languages; for this reason Common Lisp implementations strive to make the general (or full) function call as inexpensive as possible. Python goes beyond this by providing two good alternatives to full call:

• Local call resolves function references at compile time, allowing better calling sequences and optimization across function calls. See section 5.6.
• Inline expansion totally eliminates call overhead and allows many context dependent optimizations. This provides a safe and efficient implementation of operations with function semantics, eliminating the need for error-prone macro definitions or manual case analysis. Although most Common Lisp implementations support inline expansion, it becomes a more powerful tool with Python's source level optimization. See sections 5.4 and 5.8.

Generally, Python provides simple implementations for simple uses of function call, rather than having only a single calling convention. These features allow a more natural programming style:

• Proper tail recursion. See section 5.5
• Relatively efficient closures.
• A funcall that is as efficient as normal named call.
• Calls to local functions such as from labels are optimized:
  • Control transfer is a direct jump.
  • The closure environment is passed in registers rather than heap allocated.
  • Keyword arguments and multiple values are implemented more efficiently.

  See section 5.6.