使用python检查字典中是否存在键时的AttributeError

Question

I am using Python 2.7.2+, and when trying to see if a dictionary holds a given string value (named func) I get this exception:

Traceback (most recent call last):
  File "Translator.py", line 125, in <module>
    elif type == Parser.C_ARITHMETIC : parseFunc()
  File "Translator.py", line 95, in parseFunc
    if unary.has_key(func) : 
AttributeError: 'function' object has no attribute 'has_key'

This is where I define the dictionaries:

binary = {"add":'+', "sub":'-', "and":'&', "or":'|'}
relational = {"eq":"JEQ" , "lt":"JLT", "gt":"JGT"}
unary = {"neg":'-'}

Here's the function where the exception is raised:

def parseFunc():
    func = parser.arg1 
    print func  
    output.write("//pop to var1" + endLine)
    pop(var1)
    if unary.has_key(func) : // LINE 95
        unary()
        return
    output.write("//pop to var2" + endLine)
    pop(var2)
    result = "//"+func + endLine
    result += "@" + var1 + endLine
    result += "D=M" + endLine
    result += "@" + var2 + endLine
    output.write(result)
    if binary.has_key(func) : 
        binary()
    else : relational()

Also, I tried changing if unary.has_key(func) to if func in unary but then I got

Traceback (most recent call last):
  File "Translator.py", line 126, in <module>
    elif type == Parser.C_ARITHMETIC : parseFunc()
  File "Translator.py", line 95, in parseFunc
    if func in unary:
TypeError: argument of type 'function' is not iterable

Ps I tired it also using python 3.2

Any ideas? Thanks

Answer 1

In Python 3, dict.has_key() is gone (and it has been deprecated for quite some time). Use x in my_dict instead.

Your problem is a different one, though. While your definition shows unary should be a dictionary, the traceback shows it actually is a function. So somewhere in the code you did not show, unary is redefined.

And even if unary was a dictionary, you would not be able to call it.

Answer 2

It seems from your trace that you override the value of unary with a function (do you have any function called "unary"?). Therefore you are trying to call "has_key" method on a function that obviously has no such method. Pay attention with variable names, variable x will override def x() if it's placed after it in your code, and vice versa.