CODEWITHSUNDEEP
pythonr
Ben Bolker
Ben Bolker

Reputation: 226712

python equivalent of get() in R (= use string to retrieve value of symbol)

In R, the get(s) function retrieves the value of the symbol whose name is stored in the character variable (vector) s, e.g.

X <- 10
r <- "XVI"
s <- substr(r,1,1) ## "X"
get(s)             ## 10

takes the first symbol of the Roman numeral r and translates it to its integer equivalent.

Despite spending a while poking through R-Python dictionaries and Googling various combinations of "metaprogramming", "programming on the language", "symbol", "string", etc., I haven't come up with anything. (I am a very experienced R user and a novice Python user.)

(I know the example above is a (very!) poor way to approach the problem. I'm interested in the general answer to this question, not specifically in converting Roman numerals to integers ...)

Upvotes: 16

Views: 3921

Answers (2)

zw324
zw324

Reputation: 27220

You can use locals:

s = 1
locals()['s']

EDIT:

Actually, get in R is more versatile - get('as.list') will give you back as.list. For class members, in Python, we can use getattr (here), and for built-in things like len, getattr(__builtins__, 'len') works.

Upvotes: 17

mbomb007
mbomb007

Reputation: 4261

Use the eval function, which evaluates a string as an expression.

X = 10
r = "XVI"
v = eval(r[0])

Important note: eval() evaluates any code that can be used in an expression, not just variables. Do not use it directly in conjunction with user input, which could risk a security vulnerability.

Upvotes: 6

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