这份warnnings源码共有526行，其中有import进来的模块有sys模块，linecache模块，re模块，tracemalloc模块，在没有看源码前，我是还没有直接接触到或用到linecache模块和tracemalloc模块的，到今天才知道 linecache模块还可以作为读取大文件来用，网上有说法是：
import linecache
filename = 'xxxxx.txt'
line_str = linecache.getline(filename,9)
假设filename是一个非常大的文件，用linecache可以读取该大文件读到缓存中并读取到的特定行内容
就比如上面的例子，读取该txt文件第9行内容。还可以读取多行，方法如下：
lines_lst = linecache.getlines(filename) 返回的 lines_lst 是个内容列表
说是比open（）读取效率更高还有 tracemalloc是跟踪内存分配模块：https://docs.python.org/zh-cn/3.6/library/tracemalloc.html?highlight=tracemalloc#module-tracemalloc
warnnings模块源码贴出如下，官网模块解析地址：https://docs.python.org/zh-cn/3.6/library/warnings.html?highlight=warnings#available-context-managers
"""Python part of the warnings subsystem."""
import sys
__all__ = ["warn", "warn_explicit", "showwarning",
"formatwarning", "filterwarnings", "simplefilter",
"resetwarnings", "catch_warnings"]
def showwarning(message, category, filename, lineno, file=None, line=None):
"""Hook to write a warning to a file; replace if you like."""
msg = WarningMessage(message, category, filename, lineno, file, line)
_showwarnmsg_impl(msg)
def formatwarning(message, category, filename, lineno, line=None):
"""Function to format a warning the standard way."""
msg = WarningMessage(message, category, filename, lineno, None, line)
return _formatwarnmsg_impl(msg)
def _showwarnmsg_impl(msg):
file = msg.file
if file is None:
file = sys.stderr
if file is None:
# sys.stderr is None when run with pythonw.exe:
# warnings get lost
return
text = _formatwarnmsg(msg)
try:
file.write(text)
except OSError:
# the file (probably stderr) is invalid - this warning gets lost.
pass
def _formatwarnmsg_impl(msg):
s = ("%s:%s: %s: %s\n"
% (msg.filename, msg.lineno, msg.category.__name__,
msg.message))
if msg.line is None:
try:
import linecache
line = linecache.getline(msg.filename, msg.lineno)
except Exception:
# When a warning is logged during Python shutdown, linecache
# and the import machinery don't work anymore
line = None
linecache = None
else:
line = msg.line
if line:
line = line.strip()
s += " %s\n" % line
if msg.source is not None:
try:
import tracemalloc
tb = tracemalloc.get_object_traceback(msg.source)
except Exception:
# When a warning is logged during Python shutdown, tracemalloc
# and the import machinery don't work anymore
tb = None
if tb is not None:
s += 'Object allocated at (most recent call first):\n'
for frame in tb:
s += (' File "%s", lineno %s\n'
% (frame.filename, frame.lineno))
try:
if linecache is not None:
line = linecache.getline(frame.filename, frame.lineno)
else:
line = None
except Exception:
line = None
if line:
line = line.strip()
s += ' %s\n' % line
return s
# Keep a reference to check if the function was replaced
_showwarning_orig = showwarning
def _showwarnmsg(msg):
"""Hook to write a warning to a file; replace if you like."""
try:
sw = showwarning
except NameError:
pass
else:
if sw is not _showwarning_orig:
# warnings.showwarning() was replaced
if not callable(sw):
raise TypeError("warnings.showwarning() must be set to a "
"function or method")
sw(msg.message, msg.category, msg.filename, msg.lineno,
msg.file, msg.line)
return
_showwarnmsg_impl(msg)
# Keep a reference to check if the function was replaced
_formatwarning_orig = formatwarning
def _formatwarnmsg(msg):
"""Function to format a warning the standard way."""
try:
fw = formatwarning
except NameError:
pass
else:
if fw is not _formatwarning_orig:
# warnings.formatwarning() was replaced
return fw(msg.message, msg.category,
msg.filename, msg.lineno, line=msg.line)
return _formatwarnmsg_impl(msg)
def filterwarnings(action, message="", category=Warning, module="", lineno=0,
append=False):
"""Insert an entry into the list of warnings filters (at the front).
'action' -- one of "error", "ignore", "always", "default", "module",
or "once"
'message' -- a regex that the warning message must match
'category' -- a class that the warning must be a subclass of
'module' -- a regex that the module name must match
'lineno' -- an integer line number, 0 matches all warnings
'append' -- if true, append to the list of filters
"""
import re
assert action in ("error", "ignore", "always", "default", "module",
"once"), "invalid action: %r" % (action,)
assert isinstance(message, str), "message must be a string"
assert isinstance(category, type), "category must be a class"
assert issubclass(category, Warning), "category must be a Warning subclass"
assert isinstance(module, str), "module must be a string"
assert isinstance(lineno, int) and lineno >= 0, \
"lineno must be an int >= 0"
_add_filter(action, re.compile(message, re.I), category,
re.compile(module), lineno, append=append)
def simplefilter(action, category=Warning, lineno=0, append=False):
"""Insert a simple entry into the list of warnings filters (at the front).
A simple filter matches all modules and messages.
'action' -- one of "error", "ignore", "always", "default", "module",
or "once"
'category' -- a class that the warning must be a subclass of
'lineno' -- an integer line number, 0 matches all warnings
'append' -- if true, append to the list of filters
"""
assert action in ("error", "ignore", "always", "default", "module",
"once"), "invalid action: %r" % (action,)
assert isinstance(lineno, int) and lineno >= 0, \
"lineno must be an int >= 0"
_add_filter(action, None, category, None, lineno, append=append)
def _add_filter(*item, append):
# Remove possible duplicate filters, so new one will be placed
# in correct place. If append=True and duplicate exists, do nothing.
if not append:
try:
filters.remove(item)
except ValueError:
pass
filters.insert(0, item)
else:
if item not in filters:
filters.append(item)
_filters_mutated()
def resetwarnings():
"""Clear the list of warning filters, so that no filters are active."""
filters[:] = []
_filters_mutated()
class _OptionError(Exception):
"""Exception used by option processing helpers."""
pass
# Helper to process -W options passed via sys.warnoptions
def _processoptions(args):
for arg in args:
try:
_setoption(arg)
except _OptionError as msg:
print("Invalid -W option ignored:", msg, file=sys.stderr)
# Helper for _processoptions()
def _setoption(arg):
import re
parts = arg.split(':')
if len(parts) > 5:
raise _OptionError("too many fields (max 5): %r" % (arg,))
while len(parts) < 5:
parts.append('')
action, message, category, module, lineno = [s.strip()
for s in parts]
action = _getaction(action)
message = re.escape(message)
category = _getcategory(category)
module = re.escape(module)
if module:
module = module + '$'
if lineno:
try:
lineno = int(lineno)
if lineno < 0:
raise ValueError
except (ValueError, OverflowError):
raise _OptionError("invalid lineno %r" % (lineno,))
else:
lineno = 0
filterwarnings(action, message, category, module, lineno)
# Helper for _setoption()
def _getaction(action):
if not action:
return "default"
if action == "all": return "always" # Alias
for a in ('default', 'always', 'ignore', 'module', 'once', 'error'):
if a.startswith(action):
return a
raise _OptionError("invalid action: %r" % (action,))
# Helper for _setoption()
def _getcategory(category):
import re
if not category:
return Warning
if re.match("^[a-zA-Z0-9_]+$", category):
try:
cat = eval（category)
except NameError:
raise _OptionError("unknown warning category: %r" % (category,))
else:
i = category.rfind(".")
module = category[:i]
klass = category[i+1:]
try:
m = __import__(module, None, None, [klass])
except ImportError:
raise _OptionError("invalid module name: %r" % (module,))
try:
cat = getattr(m, klass)
except AttributeError:
raise _OptionError("unknown warning category: %r" % (category,))
if not issubclass(cat, Warning):
raise _OptionError("invalid warning category: %r" % (category,))
return cat
def _is_internal_frame(frame):
"""Signal whether the frame is an internal CPython implementation detail."""
filename = frame.f_code.co_filename
return 'importlib' in filename and '_bootstrap' in filename
def _next_external_frame(frame):
"""Find the next frame that doesn't involve CPython internals."""
frame = frame.f_back
while frame is not None and _is_internal_frame(frame):
frame = frame.f_back
return frame
# Code typically replaced by _warnings
def warn(message, category=None, stacklevel=1, source=None):
"""Issue a warning, or maybe ignore it or raise an exception."""
# Check if message is already a Warning object
if isinstance(message, Warning):
category = message.__class__
# Check category argument
if category is None:
category = UserWarning
if not (isinstance(category, type) and issubclass(category, Warning)):
raise TypeError("category must be a Warning subclass, "
"not '{:s}'".format(type(category).__name__))
# Get context information
try:
if stacklevel <= 1 or _is_internal_frame(sys._getframe(1)):
# If frame is too small to care or if the warning originated in
# internal code, then do not try to hide any frames.
frame = sys._getframe(stacklevel)
else:
frame = sys._getframe(1)
# Look for one frame less since the above line starts us off.
for x in range(stacklevel-1):
frame = _next_external_frame(frame)
if frame is None:
raise ValueError
except ValueError:
globals = sys.__dict__
lineno = 1
else:
globals = frame.f_globals
lineno = frame.f_lineno
if '__name__' in globals:
module = globals['__name__']
else:
module = "<string>"
filename = globals.get('__file__')
if filename:
fnl = filename.lower()
if fnl.endswith(".pyc"):
filename = filename[:-1]
else:
if module == "__main__":
try:
filename = sys.argv[0]
except AttributeError:
# embedded interpreters don't have sys.argv, see bug #839151
filename = '__main__'
if not filename:
filename = module
registry = globals.setdefault("__warningregistry__", {})
warn_explicit(message, category, filename, lineno, module, registry,
globals, source)
def warn_explicit(message, category, filename, lineno,
module=None, registry=None, module_globals=None,
source=None):
lineno = int(lineno)
if module is None:
module = filename or "<unknown>"
if module[-3:].lower() == ".py":
module = module[:-3] # XXX What about leading pathname?
if registry is None:
registry = {}
if registry.get('version', 0) != _filters_version:
registry.clear()
registry['version'] = _filters_version
if isinstance(message, Warning):
text = str(message)
category = message.__class__
else:
text = message
message = category(message)
key = (text, category, lineno)
# Quick test for common case
if registry.get(key):
return
# Search the filters
for item in filters:
action, msg, cat, mod, ln = item
if ((msg is None or msg.match(text)) and
issubclass(category, cat) and
(mod is None or mod.match(module)) and
(ln == 0 or lineno == ln)):
break
else:
action = defaultaction
# Early exit actions
if action == "ignore":
registry[key] = 1
return
# Prime the linecache for formatting, in case the
# "file" is actually in a zipfile or something.
import linecache
linecache.getlines(filename, module_globals)
if action == "error":
raise message
# Other actions
if action == "once":
registry[key] = 1
oncekey = (text, category)
if onceregistry.get(oncekey):
return
onceregistry[oncekey] = 1
elif action == "always":
pass
elif action == "module":
registry[key] = 1
altkey = (text, category, 0)
if registry.get(altkey):
return
registry[altkey] = 1
elif action == "default":
registry[key] = 1
else:
# Unrecognized actions are errors
raise RuntimeError(
"Unrecognized action (%r) in warnings.filters:\n %s" %
(action, item))
# Print message and context
msg = WarningMessage(message, category, filename, lineno, source)
_showwarnmsg(msg)
class WarningMessage(object):
_WARNING_DETAILS = ("message", "category", "filename", "lineno", "file",
"line", "source")
def __init__(self, message, category, filename, lineno, file=None,
line=None, source=None):
local_values = locals()
for attr in self._WARNING_DETAILS:
setattr(self, attr, local_values[attr])
self._category_name = category.__name__ if category else None
def __str__(self):
return ("{message : %r, category : %r, filename : %r, lineno : %s, "
"line : %r}" % (self.message, self._category_name,
self.filename, self.lineno, self.line))
class catch_warnings(object):
"""A context manager that copies and restores the warnings filter upon
exiting the context.
The 'record' argument specifies whether warnings should be captured by a
custom implementation of warnings.showwarning() and be appended to a list
returned by the context manager. Otherwise None is returned by the context
manager. The objects appended to the list are arguments whose attributes
mirror the arguments to showwarning().
The 'module' argument is to specify an alternative module to the module
named 'warnings' and imported under that name. This argument is only useful
when testing the warnings module itself.
"""
def __init__(self, *, record=False, module=None):
"""Specify whether to record warnings and if an alternative module
should be used other than sys.modules['warnings'].
For compatibility with Python 3.0, please consider all arguments to be
keyword-only.
"""
self._record = record
self._module = sys.modules['warnings'] if module is None else module
self._entered = False
def __repr__(self):
args = []
if self._record:
args.append("record=True")
if self._module is not sys.modules['warnings']:
args.append("module=%r" % self._module)
name = type(self).__name__
return "%s(%s)" % (name, ", ".join(args))
def __enter__(self):
if self._entered:
raise RuntimeError("Cannot enter %r twice" % self)
self._entered = True
self._filters = self._module.filters
self._module.filters = self._filters[:]
self._module._filters_mutated()
self._showwarning = self._module.showwarning
self._showwarnmsg_impl = self._module._showwarnmsg_impl
if self._record:
log = []
self._module._showwarnmsg_impl = log.append
# Reset showwarning() to the default implementation to make sure
# that _showwarnmsg() calls _showwarnmsg_impl()
self._module.showwarning = self._module._showwarning_orig
return log
else:
return None
def __exit__(self, *exc_info):
if not self._entered:
raise RuntimeError("Cannot exit %r without entering first" % self)
self._module.filters = self._filters
self._module._filters_mutated()
self._module.showwarning = self._showwarning
self._module._showwarnmsg_impl = self._showwarnmsg_impl
# filters contains a sequence of filter 5-tuples
# The components of the 5-tuple are:
# - an action: error, ignore, always, default, module, or once
# - a compiled regex that must match the warning message
# - a class representing the warning category
# - a compiled regex that must match the module that is being warned
# - a line number for the line being warning, or 0 to mean any line
# If either if the compiled regexs are None, match anything.
_warnings_defaults = False
try:
from _warnings import (filters, _defaultaction, _onceregistry,
warn, warn_explicit, _filters_mutated)
defaultaction = _defaultaction
onceregistry = _onceregistry
_warnings_defaults = True
except ImportError:
filters = []
defaultaction = "default"
onceregistry = {}
_filters_version = 1
def _filters_mutated():
global _filters_version
_filters_version += 1
# Module initialization
_processoptions(sys.warnoptions)
if not _warnings_defaults:
silence = [ImportWarning, PendingDeprecationWarning]
silence.append(DeprecationWarning)
for cls in silence:
simplefilter("ignore", category=cls)
bytes_warning = sys.flags.bytes_warning
if bytes_warning > 1:
bytes_action = "error"
elif bytes_warning:
bytes_action = "default"
else:
bytes_action = "ignore"
simplefilter(bytes_action, category=BytesWarning, append=1)
# resource usage warnings are enabled by default in pydebug mode
if hasattr(sys, 'gettotalrefcount'):
resource_action = "always"
else:
resource_action = "ignore"
simplefilter(resource_action, category=ResourceWarning, append=1)
del _warnings_defaults从python的源码可以看到很多细节的东西，很多东西分析源码的风格就知道了官网上和市面一些教程上为什么这样写，写的原理是什么啦。
我在分析python的一个模块时，通常会选择在交互环境下使用 dir()+help 这两个神器，很多函数不会用，查一下help就知道了，很多对象有哪些属性方法dir一下就知道了，很多东西都是记不住的，你要记住的东西，就是这个东西我知道怎么查比较快的查到就很有用了。
我的warnings模块时python 3.6.4版本的，首先在交互式环境下，import warnings 然后dir(warnings) 就会给出warnings模块所有的类和方法了，这其中，以单下划线和双下划线开头的，都是作者不想提供给外人调用的，再回头直接看代码，这些以下划线开头的函数都是 被那些其它函数调用的，真正的提供给我们外界人员使用的，它都会写再 __all__ 在这个列表中["warn", "warn_explicit", "showwarning",
"formatwarning", "filterwarnings", "simplefilter",
"resetwarnings", "catch_warnings"]，共8个，
可以从下面的一个函数和类当中，知道很多：
以showwarning函数为入口，官网是这样定义的
从源码可以看到函数和类的依赖关系为(以>符号表示依赖关系)：
showwarning>WarningMessage
>_showwarnmsg_impl>_formatwarnmsg>_formatwarnmsg_impl，从这里看出来，showwarning是属于__all__列表的，官网上可能也就是对这些函数有作使用说明
warnings模块或许对我们的作用不大，可能有些情况你不想让你的程序出现一些奇奇怪怪的警告可以使用：
import warnings
warnings.filterwarnings('ignore')def showwarning(message, category, filename, lineno, file=None, line=None):
"""Hook to write a warning to a file; replace if you like."""
msg = WarningMessage(message, category, filename, lineno, file, line)
_showwarnmsg_impl(msg)
def _showwarnmsg_impl(msg):
file = msg.file
if file is None:
file = sys.stderr
if file is None:
# sys.stderr is None when run with pythonw.exe:
# warnings get lost
return
text = _formatwarnmsg(msg)
try:
file.write(text)
except OSError:
# the file (probably stderr) is invalid - this warning gets lost.
pass
def _formatwarnmsg(msg):
"""Function to format a warning the standard way."""
try:
fw = formatwarning
except NameError:
pass
else:
if fw is not _formatwarning_orig:
# warnings.formatwarning() was replaced
return fw(msg.message, msg.category,
msg.filename, msg.lineno, line=msg.line)
return _formatwarnmsg_impl(msg)
def _formatwarnmsg_impl(msg):
s = ("%s:%s: %s: %s\n"
% (msg.filename, msg.lineno, msg.category.__name__,
msg.message))
if msg.line is None:
try:
import linecache
line = linecache.getline(msg.filename, msg.lineno)
except Exception:
# When a warning is logged during Python shutdown, linecache
# and the import machinery don't work anymore
line = None
linecache = None
else:
line = msg.line
if line:
line = line.strip()
s += " %s\n" % line
if msg.source is not None:
try:
import tracemalloc
tb = tracemalloc.get_object_traceback(msg.source)
except Exception:
# When a warning is logged during Python shutdown, tracemalloc
# and the import machinery don't work anymore
tb = None
if tb is not None:
s += 'Object allocated at (most recent call first):\n'
for frame in tb:
s += (' File "%s", lineno %s\n'
% (frame.filename, frame.lineno))
try:
if linecache is not None:
line = linecache.getline(frame.filename, frame.lineno)
else:
line = None
except Exception:
line = None
if line:
line = line.strip()
s += ' %s\n' % line
return s
class WarningMessage(object):
_WARNING_DETAILS = ("message", "category", "filename", "lineno", "file",
"line", "source")
def __init__(self, message, category, filename, lineno, file=None,
line=None, source=None):
local_values = locals()
for attr in self._WARNING_DETAILS:
setattr(self, attr, local_values[attr])
self._category_name = category.__name__ if category else None
def __str__(self):
return ("{message : %r, category : %r, filename : %r, lineno : %s, "
"line : %r}" % (self.message, self._category_name,
self.filename, self.lineno, self.line))而我在分析WarningMessage这个类时，注意到了几点：
1、_WARNING_DETAILS的命名规则很规范，单下划开头，大写字母，而且它定义的是元组类型，常量用元组序列，有安全性
2、local_values = locals() 是将局部变量以字典的形式返回， 我目前还没有用到过这个函数，所以看到这个的时候，还是去查了之后，才想起了locals()的用法，这里记录一下，说不定以后要用得到呢
3、setattr(self,attr,local_values[attr]）中setattr是给实例添加属性，相应的还有getattr(self,attr,attr_value)
4、最后是__str__这个函数，最后return 回来的这个format形式，原来源码中都是这么写的啊，我自己没有用过%s,都是用的format形式
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