Python if statement returning

Question

I am having trouble with what is presumably a simple if statement. I am trying to pass through the type of VM file format to use. Even if I put VMDK or VHD, it still comes back with VMDK is an invalid type or VHD is an invalid type.

import sys
vmtype = sys.argv[3]
vmtype = str(vmtype).strip().upper()
## File format check
if vmtype is not ("VHD") or ("VMDK"):
    print vmtype + " is an invalid type"
    sys.exit()

I have tried the if statement with != and not putting the parameters in parentheses. I have searched the web for a while and have tried what I have found and am still running into the same issue.

FYI I am running Python 2.6.5

tckmn · Accepted Answer · 2013-07-19 07:27:44Z

9

Try:

if vmtype not in ("VHD", "VMDK"):

Your current code parses as:

if (vmtype is not ("VHD")) or ("VMDK"):

Which is obviously wrong. Since ("VMDK") is a truthy value, the whole statement always be true. Therefore the if statement will always execute.

Note that even if you tried

if vmtype is not "VHD":

It would not work, because is tests identity, not value. You would use:

if vmtype != "VHD":

edited Jul 19, 2013 at 7:27

answered Jul 19, 2013 at 7:20

tckmn

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2 Comments

user2357112 Over a year ago

Other bug: is tests object identity instead of value equality. The not in solution happens to solve that problem too, but I'm not sure whether you noticed.

Greg Over a year ago

Doorknob, the not in works great. Thank you for the insight. I am still learning Python so I am prone to rookie mistakes.

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