Check whether a path is valid in Python without creating a file at the path”s target

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I have a path (including directory and file name).
I need to test if the file-name is a valid, e.g. if the file-system will allow me to create a file with such a name.
The file-name has some unicode characters in it.

It"s safe to assume the directory segment of the path is valid and accessible (I was trying to make the question more gnerally applicable, and apparently I wen too far).

I very much do not want to have to escape anything unless I have to.

I"d post some of the example characters I am dealing with, but apparently they get automatically removed by the stack-exchange system. Anyways, I want to keep standard unicode entities like ö, and only escape things which are invalid in a filename.


Here is the catch. There may (or may not) already be a file at the target of the path. I need to keep that file if it does exist, and not create a file if it does not.

Basically I want to check if I could write to a path without actually opening the path for writing (and the automatic file creation/file clobbering that typically entails).

As such:

try:
    open(filename, "w")
except OSError:
    # handle error here

from here

Is not acceptable, because it will overwrite the existent file, which I do not want to touch (if it"s there), or create said file if it"s not.

I know I can do:

if not os.access(filePath, os.W_OK):
    try:
        open(filePath, "w").close()
        os.unlink(filePath)
    except OSError:
        # handle error here

But that will create the file at the filePath, which I would then have to os.unlink.

In the end, it seems like it"s spending 6 or 7 lines to do something that should be as simple as os.isvalidpath(filePath) or similar.


As an aside, I need this to run on (at least) Windows and MacOS, so I"d like to avoid platform-specific stuff.

’’

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Check whether a path is valid in Python without creating a file at the path"s target cos: Questions

cos

How do I install pip on macOS or OS X?

5 answers

I spent most of the day yesterday searching for a clear answer for installing pip (package manager for Python). I can"t find a good solution.

How do I install it?

1672

Answer #1

UPDATE (Jan 2019):

easy_install has been deprecated. Please use get-pip.py instead.


Old answer:

easy_install pip

If you need admin privileges to run this, try:

sudo easy_install pip

1672

Answer #2

⚡️ TL;DR — One line solution.

All you have to do is:

sudo easy_install pip

2019: ⚠️easy_install has been deprecated. Check Method #2 below for preferred installation!

Details:

⚡️ OK, I read the solutions given above, but here"s an EASY solution to install pip.

MacOS comes with Python installed. But to make sure that you have Python installed open the terminal and run the following command.

python --version

If this command returns a version number that means Python exists. Which also means that you already have access to easy_install considering you are using macOS/OSX.

ℹ️ Now, all you have to do is run the following command.

sudo easy_install pip

After that, pip will be installed and you"ll be able to use it for installing other packages.

Let me know if you have any problems installing pip this way.

Cheers!

P.S. I ended up blogging a post about it. QuickTip: How Do I Install pip on macOS or OS X?


✅ UPDATE (Jan 2019): METHOD #2: Two line solution —

easy_install has been deprecated. Please use get-pip.py instead.

First of all download the get-pip file

curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py

Now run this file to install pip

python get-pip.py

That should do it.

Another gif you said? Here ya go!

1672

Answer #3

You can install it through Homebrew on OS X. Why would you install Python with Homebrew?

The version of Python that ships with OS X is great for learning but it’s not good for development. The version shipped with OS X may be out of date from the official current Python release, which is considered the stable production version. (source)

Homebrew is something of a package manager for OS X. Find more details on the Homebrew page. Once Homebrew is installed, run the following to install the latest Python, Pip & Setuptools:

brew install python

How can I open multiple files using "with open" in Python?

5 answers

I want to change a couple of files at one time, iff I can write to all of them. I"m wondering if I somehow can combine the multiple open calls with the with statement:

try:
  with open("a", "w") as a and open("b", "w") as b:
    do_something()
except IOError as e:
  print "Operation failed: %s" % e.strerror

If that"s not possible, what would an elegant solution to this problem look like?

788

Answer #1

As of Python 2.7 (or 3.1 respectively) you can write

with open("a", "w") as a, open("b", "w") as b:
    do_something()

In earlier versions of Python, you can sometimes use contextlib.nested() to nest context managers. This won"t work as expected for opening multiples files, though -- see the linked documentation for details.


In the rare case that you want to open a variable number of files all at the same time, you can use contextlib.ExitStack, starting from Python version 3.3:

with ExitStack() as stack:
    files = [stack.enter_context(open(fname)) for fname in filenames]
    # Do something with "files"

Most of the time you have a variable set of files, you likely want to open them one after the other, though.

open() in Python does not create a file if it doesn"t exist

5 answers

What is the best way to open a file as read/write if it exists, or if it does not, then create it and open it as read/write? From what I read, file = open("myfile.dat", "rw") should do this, right?

It is not working for me (Python 2.6.2) and I"m wondering if it is a version problem, or not supposed to work like that or what.

The bottom line is, I just need a solution for the problem. I am curious about the other stuff, but all I need is a nice way to do the opening part.

The enclosing directory was writeable by user and group, not other (I"m on a Linux system... so permissions 775 in other words), and the exact error was:

IOError: no such file or directory.

778

Answer #1

You should use open with the w+ mode:

file = open("myfile.dat", "w+")

Difference between modes a, a+, w, w+, and r+ in built-in open function?

5 answers

In the python built-in open function, what is the exact difference between the modes w, a, w+, a+, and r+?

In particular, the documentation implies that all of these will allow writing to the file, and says that it opens the files for "appending", "writing", and "updating" specifically, but does not define what these terms mean.

721

Answer #1

The opening modes are exactly the same as those for the C standard library function fopen().

The BSD fopen manpage defines them as follows:

 The argument mode points to a string beginning with one of the following
 sequences (Additional characters may follow these sequences.):

 ``r""   Open text file for reading.  The stream is positioned at the
         beginning of the file.

 ``r+""  Open for reading and writing.  The stream is positioned at the
         beginning of the file.

 ``w""   Truncate file to zero length or create text file for writing.
         The stream is positioned at the beginning of the file.

 ``w+""  Open for reading and writing.  The file is created if it does not
         exist, otherwise it is truncated.  The stream is positioned at
         the beginning of the file.

 ``a""   Open for writing.  The file is created if it does not exist.  The
         stream is positioned at the end of the file.  Subsequent writes
         to the file will always end up at the then current end of file,
         irrespective of any intervening fseek(3) or similar.

 ``a+""  Open for reading and writing.  The file is created if it does not
         exist.  The stream is positioned at the end of the file.  Subse-
         quent writes to the file will always end up at the then current
         end of file, irrespective of any intervening fseek(3) or similar.

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