Convert a string to preexisting variable names

Question

How do I convert a string to the variable name in Python?

For example, if the program contains a object named self.post that contains a variable named, I want to do something like:

somefunction("self.post.id") = |Value of self.post.id|

Asked By: Mohit Ranka

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Source

Answer 1

As referenced in Stack Overflow question Inplace substitution from ConfigParser, you’re looking for eval():

print eval('self.post.id') # Prints the value of self.post.id

Answered By: Owen

Answer 2

Also, there is the globals() function in Python which returns a dictionary with all the defined variables. You could also use something like this:

print globals()["myvar"]

Answered By: Geo

Answer 3

Note: do not use eval in any case where you are getting the name to look up from user entered input. For example, if this comes from a web page, there is nothing preventing anyone from entering:

__import__("os").system("Some nasty command like rm -rf /*")

as the argument. Better is to limit to well-defined lookup locations such as a dictionary or instance using getattr(). For example, to find the “post” value on self, use:

varname = "post"
value = getattr(self, varname)  # Gets self.post

Similarly to set it, use setattr():

value = setattr(self, varname, new_value)

To handle fully qualified names, like “post.id”, you could use something like the below functions in place of getattr() / setattr().

def getattr_qualified(obj, name):
    for attr in name.split("."):
        obj = getattr(obj, attr)
    return obj

def setattr_qualified(obj, name, value):
    parts = name.split(".")
    for attr in parts[:-1]:
        obj = getattr(obj, attr)
    setattr(obj, parts[-1], value)

Answered By: Brian

Answer 4

You could do something like what Geo recommended, or go with:

>>> wine = 'pinot_noir'
>>> vars()[wine] = 'yum'
>>> pinot_noir
'yum'

~~Note: vars() and globals() are the same, I’m just used to using vars()~~
I’m surprised nobody called me out on this! Anyway, it’s vars() and locals() that are the same.

Answered By: gibson

Answer 5

Use this

var="variable name"
def returnvar(string):
    exec(f"""global rtn
rtn={string}""")
    return rtn

var will be your string and run returnvar(var) will to return variable

Answered By: Supergamer

Convert a string to preexisting variable names

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