这就是全部?让我们从一个简单的非正式 BNF 开始:
func_call ::= identifier '(' func_arg [',' func_arg]... ')'
func_arg ::= named_arg | arg_expr
named_arg ::= identifier '=' arg_expr
arg_expr ::= identifier | real | integer | dict_literal | list_literal | tuple_literal | func_call
identifier ::= (alpha|'_') (alpha|num|'_')*
alpha ::= some letter 'a'..'z' 'A'..'Z'
num ::= some digit '0'..'9'
转换为 pyparsing,自下而上工作:
identifier = Word(alphas+'_', alphanums+'_')
# definitions of real, integer, dict_literal, list_literal, tuple_literal go here
# see further text below
# define a placeholder for func_call - we don't have it yet, but we need it now
func_call = Forward()
string = pp.quotedString | pp.unicodeString
arg_expr = identifier | real | integer | string | dict_literal | list_literal | tuple_literal | func_call
named_arg = identifier + '=' + arg_expr
# to define func_arg, must first see if it is a named_arg
# why do you think this is?
func_arg = named_arg | arg_expr
# now define func_call using '<<' instead of '=', to "inject" the definition
# into the previously declared Forward
#
# Group each arg to keep its set of tokens separate, otherwise you just get one
# continuous list of parsed strings, which is almost as worthless the original
# string
func_call << identifier + '(' + delimitedList(Group(func_arg)) + ')'
这些arg_expr
元素可能需要一段时间才能完成,但幸运的是,您可以将它们从 pyparsing wiki 的示例页面中删除:http: //pyparsing.wikispaces.com/file/view/parsePythonValue.py
from parsePythonValue import (integer, real, dictStr as dict_literal,
listStr as list_literal, tupleStr as tuple_literal)
您仍然可能会使用*list_of_args
or**dict_of_named_args
表示法传递参数。扩展arg_expr
以支持这些:
deref_list = '*' + (identifier | list_literal | tuple_literal)
deref_dict = '**' + (identifier | dict_literal)
arg_expr = identifier | real | integer | dict_literal | list_literal | tuple_literal | func_call | deref_list | deref_dict
现在为自己编写一些测试用例 - 从简单开始,逐步复杂化:
sin(30)
sin(a)
hypot(a,b)
len([1,2,3])
max(*list_of_vals)
需要添加的其他参数类型arg_expr
(留作 OP 的进一步练习):
索引参数:dictval['a']
divmod(10,3)[0]
range(10)[::2]
对象属性引用:a.b.c
算术表达式 : sin(30)
,sin(a+2*b)
比较表达式:sin(a+2*b) > 0.5
10 < a < 20
布尔表达式:a or b and not (d or c and b)
拉姆达表达式:lambda x : sin(x+math.pi/2)
列表理解
生成器表达式