CODEWITHSUNDEEP
stringescaping
user4237459
user4237459

Reputation:

Escaping a string multiple times

This probably applies to all languages that have escape characters, but I'm making an example with Python (3.4.2). How would you escape this:
Warning: Do not use this code ever, this is just an example

#unescaped for examples sake, and using solely " instead of '
eval("eval("print("Hi")")")

This won't work:

>>> eval("eval(\"print(\"Hi\")\")")
Traceback (most recent call last):
  File "<pyshell#0>", line 1, in <module>
    eval("eval(\"print(\"Hi\")\")")
  File "<string>", line 1
    eval("print("Hi")")
                  ^
SyntaxError: invalid syntax

This also won't work:

>>> eval("eval(\"print(\\"Hi\\")\")")
SyntaxError: invalid syntax

So how would you escape it?

Upvotes: 0

Views: 365

Answers (1)

user4237459
user4237459

Reputation:

Escape with three backslashes (\\\)

eval("eval(\"print(\\\"Hi\\\")\")")

Explanation:
In eval("eval(\"print(\\\"Hi\\\")\")"), the string being passed is:

"eval(\"print(\\\"Hi\\\")\")"

When the string is evaluated, all the escape characters are removed. This turns "\\" into \ and "\"" into ". So, you end up with:

eval("print(\"Hi\")").

(This evaluates "print(\"Hi\")", which is just print("Hi").)

Note this:

>>> len("\\") # Escaped letters are on character
1
>>> len("\n")
1
>>> len("nn")
2
>>> "\'" == "'" == '\'' # Various forms of escaped '
True
>>> "\n" == """
""" # Multiline string with a newline
True
>>> "\q" == "q" # q is not escapeable
False
>>> "\q"
'\\q'
>>> len("\q")
2

Upvotes: 1

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