Python-Aware Python
Ned Batchelder
@nedbat
Source code
.. compiled ..
Bytecode in .pyc files
.. interpreted ..
Function objects in memory
.. executed ..
Action!
class Greeter:
def __init__(self, who):
self.who = who
def greet(self):
print "Hello, %s!" % self.who
greeter = Greeter("world")
greeter.greet()
Module(
body=[
ClassDef(
name='Greeter', bases=[],
body=[
FunctionDef(
name='__init__',
args=arguments(
args=[
Name(id='self', ctx=Param()),
Name(id='who', ctx=Param())],
vararg=None, kwarg=None, defaults=[]),
body=[
Assign(
targets=[
Attribute(
value=Name(id='self', ctx=Load()),
attr='who', ctx=Store()) ],
value=Name(id='who', ctx=Load()))],
>>> def my_fun(x=12):
... y = x * 3
... return y
...
>>> code_obj = my_fun.func_code
>>> code_obj.co_name
'my_fun'
>>> code_obj.co_filename
'<stdin>'
>>> code_obj.co_argcount
1
>>> code_obj.co_varnames
('x', 'y')
>>> code_obj.co_consts
(None, 3)
>>> code_obj.co_code
'|\x00\x00d\x01\x00\x14}\x01\x00|\x01\x00S'
>>> def my_fun(x=12):
... y = x * 3
... return y
...
>>> my_fun.func_code
<code object my_fun at 000000000217A918, file "<stdin>", line 1>
>>> my_fun.func_name
'my_fun'
>>> my_fun.func_defaults
(12,)
>>> my_fun.func_defaults = (27,)
>>> my_fun()
81
Traceback (most recent call last):
File "oops.py", line 10, in
i_hope_it_works(17)
File "oops.py", line 8, in i_hope_it_works
try_it(x)
File "oops.py", line 5, in try_it
try_again(x)
File "oops.py", line 2, in try_again
raise Exception("oops")
Exception: oops
import sys
def trace(frame, event, arg):
filename = frame.f_code.co_filename
lineno = frame.f_lineno
print "%s @ %s: %s" % (filename, lineno, event)
return trace
def run_py(py_file):
sys.settrace(trace)
exec open(py_file) in {}
sys.settrace(None)
if __name__ == '__main__':
run_py(sys.argv[1])
greeter.py @ 1: call
greeter.py @ 1: line
greeter.py @ 1: call
greeter.py @ 1: line
greeter.py @ 2: line
greeter.py @ 5: line
greeter.py @ 5: return
greeter.py @ 8: line
greeter.py @ 2: call
greeter.py @ 3: line
greeter.py @ 3: return
greeter.py @ 9: line
greeter.py @ 5: call
greeter.py @ 6: line
Hello, world!
greeter.py @ 6: return
greeter.py @ 9: return
import linecache, sys
class ShowAndTell(object):
def __init__(self):
self.nest = 0
def trace_fn(self, frame, event, arg):
filename = frame.f_code.co_filename
lineno = frame.f_lineno
indent = " " * self.nest
info = "%s%s @ %s: %s" % (indent, filename, lineno, event)
src = linecache.getline(filename, lineno)
print "%-30s | %s" % (info, src[:-1])
if event == "call":
self.nest += 1
elif event == "return":
self.nest -= 1
return self.trace_fn
greeter.py @ 1: call | class Greeter:
greeter.py @ 1: line | class Greeter:
greeter.py @ 1: call | class Greeter:
greeter.py @ 1: line | class Greeter:
greeter.py @ 2: line | def __init__(self, who):
greeter.py @ 5: line | def greet(self):
greeter.py @ 5: return | def greet(self):
greeter.py @ 8: line | greeter = Greeter("world")
greeter.py @ 2: call | def __init__(self, who):
greeter.py @ 3: line | self.who = who
greeter.py @ 3: return | self.who = who
greeter.py @ 9: line | greeter.greet()
greeter.py @ 5: call | def greet(self):
greeter.py @ 6: line | print "Hello, %s!" % self.who
Hello, world!
greeter.py @ 6: return | print "Hello, %s!" % self.who
greeter.py @ 9: return | greeter.greet()
class Greeter:
def __init__(self, who):
self.who = who
def greet(self):
print "Hello, %s!" % self.who
greeter = Greeter("world")
greeter.greet()
class MyAstVisitor(ast.NodeVisitor):
def visit_Expr(self, node):
# .. do something with Expr node ..
def visit_Assignment(self, node):
# .. do something with Assignment node ..
# .. other visit_XXX as needed ..
class ExpressionFinder(ast.NodeVisitor):
def visit_Str(self, node):
return repr(node.s)
def visit_Name(self, node):
self.add_expr(node, node.id)
return node.id
def visit_BinOp(self, node):
left = self.visit(node.left)
right = self.visit(node.right)
if left and right:
expr = "(%s %s %s)" % (left, self.op(node.op), right)
self.add_expr(node, expr)
return expr
# .. 10 more node types ..
class ExpressionFinder(ast.NodeVisitor):
# .. continued ..
def add_expr(self, node, expr):
"""Add the expression `expr` found in node `node`."""
self.exprs[node.lineno].add(expr)
def expressions(self, node):
"""Return a dict mapping line numbers to expressions."""
self.exprs = collections.defaultdict(set)
self.visit(node)
return self.exprs
def line_expressions(filename):
source = open(filename).read()
node = ast.parse(source, mode="exec")
return ExpressionFinder().expressions(node)
class ShowAndTell(object):
#...
def trace_fn(self, frame, event, arg):
#...
vals = []
for expr in self.expressions(filename, lineno):
try:
val = eval(expr, frame.f_globals, frame.f_locals)
vals.append((expr, val))
except:
# Eval'ing can die, just move on.
pass
if vals:
print
print "\n".join(":: %s : %r" % ev for ev in vals)
print
greeter.py @ 1: call | class Greeter:
greeter.py @ 1: line | class Greeter:
greeter.py @ 1: call | class Greeter:
greeter.py @ 1: line | class Greeter:
greeter.py @ 2: line | def __init__(self, who):
greeter.py @ 5: line | def greet(self):
greeter.py @ 5: return | def greet(self):
greeter.py @ 8: line | greeter = Greeter("world")
:: Greeter : <class __builtin__.Greeter at 0x000000000200E780>
greeter.py @ 2: call | def __init__(self, who):
:: who : 'world'
:: self : <__builtin__.Greeter instance at 0x000000000202B608>
greeter.py @ 3: line | self.who = who
:: who : 'world'
:: self : <__builtin__.Greeter instance at 0x000000000202B608>
greeter.py @ 3: return | self.who = who
:: who : 'world'
:: self : <__builtin__.Greeter instance at 0x000000000202B608>
:: self.who : 'world'
greeter.py @ 9: line | greeter.greet()
:: self.who : 'world'
greeter.py @ 9: line | greeter.greet()
:: greeter : <__builtin__.Greeter instance at 0x000000000202B608>
:: greeter.greet : <bound method Greeter.greet of <__builtin__.Greeter instance at 0x000000000202B608>>
greeter.py @ 5: call | def greet(self):
:: self : <__builtin__.Greeter instance at 0x000000000202B608>
greeter.py @ 6: line | print "Hello, %s!" % self.who
:: self : <__builtin__.Greeter instance at 0x000000000202B608>
:: self.who : 'world'
:: ('Hello, %s!' % self.who) : 'Hello, world!'
Hello, world!
greeter.py @ 6: return | print "Hello, %s!" % self.who
:: self : <__builtin__.Greeter instance at 0x000000000202B608>
:: self.who : 'world'
:: ('Hello, %s!' % self.who) : 'Hello, world!'
greeter.py @ 9: return | greeter.greet()
:: greeter : <__builtin__.Greeter instance at 0x000000000202B608>
:: greeter.greet : <bound method Greeter.greet of <__builtin__.Greeter instance at 0x000000000202B608>>
def should_show_value(self, expr, val):
if inspect.isroutine(val):
return False
if inspect.isclass(val):
return False
return True
def trace_fn(self, frame, event, arg):
#...
vals = []
for expr in self.expressions(filename, lineno):
try:
val = eval(expr, frame.f_globals, frame.f_locals)
if self.should_show_value(expr, val):
vals.append((expr, val))
except:
# Eval'ing can die, just move on.
pass
if vals:
print
print "\n".join(":: %s : %r" % ev for ev in vals)
print
#...
greeter.py @ 1: call | class Greeter:
greeter.py @ 1: line | class Greeter:
greeter.py @ 1: call | class Greeter:
greeter.py @ 1: line | class Greeter:
greeter.py @ 2: line | def __init__(self, who):
greeter.py @ 5: line | def greet(self):
greeter.py @ 5: return | def greet(self):
greeter.py @ 8: line | greeter = Greeter("world")
greeter.py @ 2: call | def __init__(self, who):
:: who : 'world'
:: self : <__builtin__.Greeter instance at 0x0000000002108F48>
greeter.py @ 3: line | self.who = who
:: who : 'world'
:: self : <__builtin__.Greeter instance at 0x0000000002108F48>
greeter.py @ 3: return | self.who = who
:: who : 'world'
:: self : <__builtin__.Greeter instance at 0x0000000002108F48>
:: self.who : 'world'
greeter.py @ 9: line | greeter.greet()
:: greeter : <__builtin__.Greeter instance at 0x0000000002108F48>
greeter.py @ 5: call | def greet(self):
reader = open(filename, 'r').readline
for typ, tok, (sr, sc), (er, ec), line in tokenize.generate_tokens(reader):
#.. do something with each token ..
$ python -m dis greeter.py
1 0 LOAD_CONST 0 ('Greeter')
3 LOAD_CONST 4 (())
6 LOAD_CONST 1 (<code object Greeter at 00000000023D34E0, file "greeter.py", line 1>)
9 MAKE_FUNCTION 0
12 CALL_FUNCTION 0
15 BUILD_CLASS
16 STORE_NAME 0 (Greeter)
8 19 LOAD_NAME 0 (Greeter)
22 LOAD_CONST 2 ('world')
25 CALL_FUNCTION 1
28 STORE_NAME 1 (greeter)
9 31 LOAD_NAME 1 (greeter)
34 LOAD_ATTR 2 (greet)
37 CALL_FUNCTION 0
40 POP_TOP
41 LOAD_CONST 3 (None)
44 RETURN_VALUE
class Chameleon(object):
def __init__(self, other):
self.other = other
def __getattr__(self, name):
return getattr(self.other, name)
import os
if os.environ["EXTRA_LOGGING"]:
import my_logger
my_logger.init()
...
:: greeter : <__builtin__.Greeter instance at 0x00000000023A3E88>
# Example: Breaking out from a deeply nested loop:
from goto import goto, label
for i in range(1, 10):
for j in range(1, 20):
for k in range(1, 30):
print i, j, k
if k == 3:
goto .end
label .end
print "Finished\n"
def get_request():
"""Find the nearest caller's first "request" arg."""
try:
for f in inspect.stack():
frame = f[0]
code = frame.f_code
if code.co_argcount > 0 and code.co_varnames[0] == "request":
return frame.f_locals['request']
finally:
del frame
PS: I'm available for freelance work :)
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