CODEWITHSUNDEEP
pythonnegation
David Mulder
David Mulder

Reputation: 8017

Negation in Python

I'm trying to create a directory if the path doesn't exist, but the ! (not) operator doesn't work. I'm not sure how to negate in Python... What's the correct way to do this?

if (!os.path.exists("/usr/share/sounds/blues")):
        proc = subprocess.Popen(["mkdir", "/usr/share/sounds/blues"])
        proc.wait()

Upvotes: 218

Views: 409781

Answers (4)

chmullig
chmullig

Reputation: 13406

Combining the input from everyone else (use not, no parens, use os.mkdir) you'd get...

special_path_for_john = "/usr/share/sounds/blues"
if not os.path.exists(special_path_for_john):
    os.mkdir(special_path_for_john)

Upvotes: 3

Karl Nicoll
Karl Nicoll

Reputation: 16419

The negation operator in Python is not. Therefore just replace your ! with not.

For your example, do this:

if not os.path.exists("/usr/share/sounds/blues") :
    proc = subprocess.Popen(["mkdir", "/usr/share/sounds/blues"])
    proc.wait()

For your specific example (as Neil said in the comments), you don't have to use the subprocess module, you can simply use os.mkdir() to get the result you need, with added exception handling goodness.

Example:

blues_sounds_path = "/usr/share/sounds/blues"
if not os.path.exists(blues_sounds_path):
    try:
        os.mkdir(blues_sounds_path)
    except OSError:
        # Handle the case where the directory could not be created.

Upvotes: 300

mshell_lauren
mshell_lauren

Reputation: 5236

try instead:

if not os.path.exists(pathName):
    do this

Upvotes: 16

Cat Plus Plus
Cat Plus Plus

Reputation: 129774

Python prefers English keywords to punctuation. Use not x, i.e. not os.path.exists(...). The same thing goes for && and || which are and and or in Python.

Upvotes: 39

Related Questions