选择基于正则表达式调用的Python函数

Question

是否可以将函数放在数据结构中,而不是先给它命名def？

# This is the behaviour I want. Prints "hi".
def myprint(msg):
    print msg
f_list = [ myprint ]
f_list[0]('hi')
# The word "myprint" is never used again. Why litter the namespace with it?

lambda函数的主体受到严格限制,所以我不能使用它们.

编辑:作为参考,这更像是我遇到问题的现实代码.

def handle_message( msg ):
    print msg
def handle_warning( msg ):
    global num_warnings, num_fatals
    num_warnings += 1
    if ( is_fatal( msg ) ):
        num_fatals += 1
handlers = (
    ( re.compile( '^<\w+> (.*)' ), handle_message ),
    ( re.compile( '^\*{3} (.*)' ), handle_warning ),
)
# There are really 10 or so handlers, of similar length.
# The regexps are uncomfortably separated from the handler bodies,
# and the code is unnecessarily long.

for line in open( "log" ):
    for ( regex, handler ) in handlers:
        m = regex.search( line )
        if ( m ): handler( m.group(1) )

Answer 1

这是基于Udi的好答案.

我认为创建匿名函数的难度有点像红鲱鱼.你真正想做的是将相关代码保持在一起,并使代码整洁.所以我认为装饰师可能适合你.

import re

# List of pairs (regexp, handler)
handlers = []

def handler_for(regexp):
    """Declare a function as handler for a regular expression."""
    def gethandler(f):
        handlers.append((re.compile(regexp), f))
        return f
    return gethandler

@handler_for(r'^<\w+> (.*)')
def handle_message(msg):
    print msg

@handler_for(r'^\*{3} (.*)')
def handle_warning(msg):
    global num_warnings, num_fatals
    num_warnings += 1
    if is_fatal(msg):
        num_fatals += 1

Answer 2

更好的DRY方式来解决您的实际问题:

def message(msg):
    print msg
message.re = '^<\w+> (.*)'

def warning(msg):
    global num_warnings, num_fatals
    num_warnings += 1
    if ( is_fatal( msg ) ):
        num_fatals += 1
warning.re = '^\*{3} (.*)'

handlers = [(re.compile(x.re), x) for x in [
        message,
        warning,
        foo,
        bar,
        baz,
    ]]

Answer 3

使用模块化自包含解决方案继续Gareth的清洁方法:

import re

# in util.py
class GenericLogProcessor(object):

    def __init__(self):
      self.handlers = [] # List of pairs (regexp, handler)

    def register(self, regexp):
        """Declare a function as handler for a regular expression."""
        def gethandler(f):
            self.handlers.append((re.compile(regexp), f))
            return f
        return gethandler

    def process(self, file):
        """Process a file line by line and execute all handlers by registered regular expressions"""
        for line in file:
            for regex, handler in self.handlers:
                m = regex.search(line)
                if (m):
                  handler(m.group(1))      

# in log_processor.py
log_processor = GenericLogProcessor()

@log_processor.register(r'^<\w+> (.*)')
def handle_message(msg):
    print msg

@log_processor.register(r'^\*{3} (.*)')
def handle_warning(msg):
    global num_warnings, num_fatals
    num_warnings += 1
    if is_fatal(msg):
        num_fatals += 1

# in your code
with open("1.log") as f:
  log_processor.process(f)

Answer 4

如果要保持干净的命名空间,请使用del:

def myprint(msg):
    print msg
f_list = [ myprint ]
del myprint
f_list[0]('hi')

Answer 5

如你所说,这是不可能做到的.但你可以近似它.

def create_printer():
  def myprint(x):
    print x
  return myprint

x = create_printer()

myprint这里实际上是匿名的,因为调用者无法再访问创建它的变量范围.(参见Python中的闭包.)

Answer 6

如果您担心污染命名空间,请在另一个函数内创建函数.然后你只是"污染" create_functions函数的本地命名空间而不是外部命名空间.

def create_functions():
    def myprint(msg):
        print msg
    return [myprint]

f_list = create_functions()
f_list[0]('hi')

Answer 7

你不应该这样做，因为 eval 是邪恶的，但你可以在运行时使用FunctionTypeand编译函数代码compile：

>>> def f(msg): print msg
>>> type(f)
 <type 'function'>
>>> help(type(f))
...
class function(object)
 |  function(code, globals[, name[, argdefs[, closure]]])
 |
 |  Create a function object from a code object and a dictionary.
 |  The optional name string overrides the name from the code object.
 |  The optional argdefs tuple specifies the default argument values.
 |  The optional closure tuple supplies the bindings for free variables.    
...

>>> help(compile)
Help on built-in function compile in module __builtin__:

compile(...)
    compile(source, filename, mode[, flags[, dont_inherit]]) -> code object

    Compile the source string (a Python module, statement or expression)
    into a code object that can be executed by the exec statement or eval().
    The filename will be used for run-time error messages.
    The mode must be 'exec' to compile a module, 'single' to compile a
    single (interactive) statement, or 'eval' to compile an expression.
    The flags argument, if present, controls which future statements influence
    the compilation of the code.
    The dont_inherit argument, if non-zero, stops the compilation inheriting
    the effects of any future statements in effect in the code calling
    compile; if absent or zero these statements do influence the compilation,
    in addition to any features explicitly specified.