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codeop Module Complexity¶
The codeop module is the compile step of an interactive interpreter: it decides whether a piece
of source is a complete statement, an incomplete one that needs another line, or a syntax error,
and it can remember __future__ statements from one input to the next. Every call compiles the
source it is given from scratch.
n is the length of the source passed to one call. The compiler's own work - parsing, building
the syntax tree and the code object - is O(n), and so is everything here that compiles.
Complexity Reference¶
compile_command¶
| Operation | Time | Space | Notes |
|---|---|---|---|
codeop.compile_command(source, filename="<input>", symbol="single") |
O(n) | O(n) | A code object for complete input, None for incomplete input, SyntaxError for invalid input; remembers nothing between calls |
Compile¶
| Operation | Time | Space | Notes |
|---|---|---|---|
codeop.Compile() |
O(1) | O(1) | |
Calling a Compile instance: compiler(source, filename, symbol) |
O(n) | O(n) | Takes the source, filename and mode arguments of the built-in compile(); __future__ statements it has compiled stay in force for later calls |
CommandCompiler¶
| Operation | Time | Space | Notes |
|---|---|---|---|
codeop.CommandCompiler() |
O(1) | O(1) | |
Calling a CommandCompiler instance: compiler(source, filename="<input>", symbol="single") |
O(n) | O(n) | Answers as compile_command() does, and remembers __future__ statements like Compile |
Checking Whether Input Is Complete¶
An interactive loop compiles everything typed so far each time a line arrives, so each line costs O(n) in the statement entered so far, not just in the new line.
import codeop
code = codeop.compile_command('print("hello")') # O(n)
assert code is not None
assert codeop.compile_command("if True:") is None # O(n): needs another line
try:
codeop.compile_command("if True") # O(n)
except SyntaxError:
pass
else:
raise AssertionError("an invalid statement should raise SyntaxError")
Remembering __future__ Statements¶
compile_command() starts afresh on every call. A CommandCompiler - or a Compile, for the
source, filename and mode arguments of compile() - keeps the compiler flags that a __future__ statement turned on and
applies them to every later input, which is what an interpreter session needs.
import __future__
import codeop
flag = __future__.annotations.compiler_flag
session = codeop.CommandCompiler()
session("from __future__ import annotations") # O(n)
assert session("x = 1").co_flags & flag # still in force
assert not codeop.compile_command("x = 1").co_flags & flag # forgotten
compiler = codeop.Compile()
compiler("from __future__ import annotations", "<input>", "exec") # O(n)
assert compiler("x = 1", "<input>", "exec").co_flags & flag