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"""Generate random Python for testing."""
import collections
from itertools import cycle, product
import random
import re
from coverage.parser import PythonParser
class PythonSpinner:
"""Spin Python source from a simple AST."""
def __init__(self):
self.lines = []
self.lines.append("async def func():")
self.indent = 4
@property
def lineno(self):
return len(self.lines) + 1
@classmethod
def generate_python(cls, ast):
spinner = cls()
spinner.gen_python_internal(ast)
return "\n".join(spinner.lines)
def add_line(self, line):
g = f"g{self.lineno}"
self.lines.append(' ' * self.indent + line.format(g=g, lineno=self.lineno))
def add_block(self, node):
self.indent += 4
self.gen_python_internal(node)
self.indent -= 4
def maybe_block(self, node, nodei, keyword):
if len(node) > nodei and node[nodei] is not None:
self.add_line(keyword + ":")
self.add_block(node[nodei])
def gen_python_internal(self, ast):
for node in ast:
if isinstance(node, list):
op = node[0]
if op == "if":
self.add_line("if {g}:")
self.add_block(node[1])
self.maybe_block(node, 2, "else")
elif op == "for":
self.add_line("for x in {g}:")
self.add_block(node[1])
self.maybe_block(node, 2, "else")
elif op == "while":
self.add_line("while {g}:")
self.add_block(node[1])
self.maybe_block(node, 2, "else")
elif op == "try":
self.add_line("try:")
self.add_block(node[1])
# 'except' clauses are different, because there can be any
# number.
if len(node) > 2 and node[2] is not None:
for except_node in node[2]:
self.add_line(f"except Exception{self.lineno}:")
self.add_block(except_node)
self.maybe_block(node, 3, "else")
self.maybe_block(node, 4, "finally")
elif op == "with":
self.add_line("with {g} as x:")
self.add_block(node[1])
else:
raise Exception(f"Bad list node: {node!r}")
else:
op = node
if op == "assign":
self.add_line("x = {lineno}")
elif op in ["break", "continue"]:
self.add_line(op)
elif op == "return":
self.add_line("return")
elif op == "yield":
self.add_line("yield {lineno}")
else:
raise Exception(f"Bad atom node: {node!r}")
def weighted_choice(rand, choices):
"""Choose from a list of [(choice, weight), ...] options, randomly."""
total = sum(w for c, w in choices)
r = rand.uniform(0, total)
upto = 0
for c, w in choices:
if upto + w >= r:
return c
upto += w
assert False, "Shouldn't get here"
class RandomAstMaker:
def __init__(self, seed=None):
self.r = random.Random()
if seed is not None:
self.r.seed(seed)
self.depth = 0
self.bc_allowed = set()
def roll(self, prob=0.5):
return self.r.random() <= prob
def choose(self, choices):
"""Roll the dice to choose an option."""
return weighted_choice(self.r, choices)
STMT_CHOICES = [
[("if", 10), ("for", 10), ("try", 10), ("while", 3), ("with", 10), ("assign", 20), ("return", 1), ("yield", 0)],
[("if", 10), ("for", 10), ("try", 10), ("while", 3), ("with", 10), ("assign", 40), ("return", 1), ("yield", 0), ("break", 10), ("continue", 10)],
[("if", 10), ("for", 10), ("try", 10), ("while", 3), ("with", 10), ("assign", 40), ("return", 1), ("yield", 0), ("break", 10), ("continue", 10)],
[("if", 10), ("for", 10), ("try", 10), ("while", 3), ("with", 10), ("assign", 40), ("return", 1), ("yield", 0), ("break", 10), ("continue", 10)],
[("if", 10), ("for", 10), ("try", 10), ("while", 3), ("with", 10), ("assign", 40), ("return", 1), ("yield", 0), ("break", 10), ("continue", 10)],
# Last element has to have no compound statements, to limit depth.
[("assign", 10), ("return", 1), ("yield", 0), ("break", 10), ("continue", 10)],
]
def make_body(self, parent):
body = []
choices = self.STMT_CHOICES[self.depth]
self.depth += 1
nstmts = self.choose([(1, 10), (2, 25), (3, 10), (4, 10), (5, 5)])
for _ in range(nstmts):
stmt = self.choose(choices)
if stmt == "if":
body.append(["if", self.make_body("if")])
if self.roll():
body[-1].append(self.make_body("ifelse"))
elif stmt == "for":
old_allowed = self.bc_allowed
self.bc_allowed = self.bc_allowed | {"break", "continue"}
body.append(["for", self.make_body("for")])
self.bc_allowed = old_allowed
if self.roll():
body[-1].append(self.make_body("forelse"))
elif stmt == "while":
old_allowed = self.bc_allowed
self.bc_allowed = self.bc_allowed | {"break", "continue"}
body.append(["while", self.make_body("while")])
self.bc_allowed = old_allowed
if self.roll():
body[-1].append(self.make_body("whileelse"))
elif stmt == "try":
else_clause = self.make_body("try") if self.roll() else None
old_allowed = self.bc_allowed
self.bc_allowed = self.bc_allowed - {"continue"}
finally_clause = self.make_body("finally") if self.roll() else None
self.bc_allowed = old_allowed
if else_clause:
with_exceptions = True
elif not else_clause and not finally_clause:
with_exceptions = True
else:
with_exceptions = self.roll()
if with_exceptions:
num_exceptions = self.choose([(1, 50), (2, 50)])
exceptions = [self.make_body("except") for _ in range(num_exceptions)]
else:
exceptions = None
body.append(
["try", self.make_body("tryelse"), exceptions, else_clause, finally_clause]
)
elif stmt == "with":
body.append(["with", self.make_body("with")])
elif stmt == "return":
body.append(stmt)
break
elif stmt == "yield":
body.append("yield")
elif stmt in ["break", "continue"]:
if stmt in self.bc_allowed:
# A break or continue immediately after a loop is not
# interesting. So if we are immediately after a loop, then
# insert an assignment.
if not body and (parent in ["for", "while"]):
body.append("assign")
body.append(stmt)
break
else:
stmt = "assign"
if stmt == "assign":
# Don't put two assignments in a row, there's no point.
if not body or body[-1] != "assign":
body.append("assign")
self.depth -= 1
return body
def async_alternatives(source):
parts = re.split(r"(for |with )", source)
nchoices = len(parts) // 2
#print("{} choices".format(nchoices))
def constant(s):
return [s]
def maybe_async(s):
return [s, "async "+s]
choices = [f(x) for f, x in zip(cycle([constant, maybe_async]), parts)]
for result in product(*choices):
source = "".join(result)
yield source
def compare_alternatives(source):
all_all_arcs = collections.defaultdict(list)
for i, alternate_source in enumerate(async_alternatives(source)):
parser = PythonParser(alternate_source)
arcs = parser.arcs()
all_all_arcs[tuple(arcs)].append((i, alternate_source))
return len(all_all_arcs)
def show_a_bunch():
longest = ""
for i in range(100):
maker = RandomAstMaker(i)
source = PythonSpinner.generate_python(maker.make_body("def"))
try:
print("-"*80, "\n", source, sep="")
compile(source, "<string>", "exec")
except Exception as ex:
print(f"Oops: {ex}\n{source}")
if len(source) > len(longest):
longest = source
def show_alternatives():
for i in range(1000):
maker = RandomAstMaker(i)
source = PythonSpinner.generate_python(maker.make_body("def"))
nlines = len(source.splitlines())
if nlines < 15:
nalt = compare_alternatives(source)
if nalt > 1:
print(f"--- {nlines:3} lines, {nalt:2} alternatives ---------")
print(source)
def show_one():
maker = RandomAstMaker()
source = PythonSpinner.generate_python(maker.make_body("def"))
print(source)
if __name__ == "__main__":
show_one()
#show_alternatives()
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