在python中使用正则表达式解析语句字符串以获取参数

Question

I have user input statements which I would like to parse for arguments. If possible using regex.

I have read much about functools.partial on Stackoverflow where I could not find argument parsing. Also in regex on Stackoverflow I could not find how to check for a match, but exclude the used tokens. The Python tokenizer seems to heavy for my purpose.

import re

def getarguments(statement):      
    prog = re.compile("([(].*[)])")
    result = prog.search(statement) 
    m = result.group()  
    # m = '(interval=1, percpu=True)'
    # or m = "('/')"
    # strip the parentheses, ugly but it works
    return statement[result.start()+1:result.end()-1] 

stm = 'psutil.cpu_percent(interval=1, percpu=True)'
arg_list = getarguments(stm) 
print(arg_list) # returns : interval=1, percpu=True

# But combining single and double quotes like
stm = "psutil.disk_usage('/').percent"
arg_list = getarguments(stm) # in debug value is "'/'"   
print(arg_list) # when printed value is : '/'

callfunction = psutil.disk_usage
args = []
args.append(arg_list)
# args.append('/')
funct1 = functools.partial(callfunction, *args)
perc = funct1().percent
print(perc)  

This results an error : builtins.FileNotFoundError: [Errno 2] No such file or directory: "'/'"

But

callfunction = psutil.disk_usage
args = []
#args.append(arg_list)
args.append('/')
funct1 = functools.partial(callfunction, *args)
perc = funct1().percent
print(perc)  

Does return (for me) 20.3 This is correct. So there is somewhere a difference.

The weird thing is, if I view the content in my IDE (WingIDE) the result is "'/'" and then, if I want to view the details then the result is '/'

I use Python 3.4.0 What is happening here, and how to solve? Your help is really appreciated.

Answer 1

getarguments("psutil.disk_usage('/').percent") returns '/' . You can check this by printing len(arg_list) , for example.

Your IDE adds " , because by default strings are enclosed into single quotes ' . Now you have a string which actually contains ' , so IDE uses double quotes to enclose the string.

Note, that '/' is not equal to "'/'" . The former is a string of 1 character, the latter is a string of 3 characters. So in order to get things right you need to strip quotes (both double and single ones) in getarguments . You can do it with following snippet

if (s.startswith('\'') and s.endswith('\'')) or 
        (s.startswith('\"') and s.endswith('\"')):
   s = s[1:-1]