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Some sensitive filenames cause failure of loading data

In using keras.model.load_weights, by the way, the weight file is saved in a hdf5 format, I come across some situations where the folder names that have initial r or t, cause the error: errno = 22, error message = 'invalid argument', flags = 0, o_flags = 0.
I want to know if there are some specified rules on the filenames which should be avoided and otherwise would lead to such reading error in python, or the situation I encountered is only specific to keras.

It would greatly help debug this if you include examples of such filenames that give you trouble. However, I have a good idea on what is probably happening here.
This problems seem to appear on folders that start with r or t on their names. Also, as they are folders, on their full path name they are preceded by a \ character (for example "\thisFolder", or similar). This is true in the case of a Windows environment, as they use \ for separating paths contrary to *nix systems that use the regular slash /.
Considering these things, seems that perhaps you are experiencing this as \r and \t are both special characters that mean Carriage Return and Tabulation, respectively. If this is the case many file openers will have trouble processing such file name.
Even more, I would not be surprised if you got the same errors on folders that begin with n or other letters that when concatenated to a backslash give special characters (\n is new line, \s is a white space, etc.).
To overcome this seems that you will need to escape your backslash character before passing it as a filename. In python, an escaped backslash is "\\"
. In addition, you can also opt to pass a Raw string instead, by adding the r prefix to your string, something like r"\a\raw\string". More information on escaping and raw string can be found on this question and answers.
I want to know if there are some specified rules on the filenames which should be avoided and otherwise would lead to such reading error in python,
As mentioned, you should avoid this with characters that have a special meaning with a backslash. I suggest you check here to see the characters Python accepts like this, so you can refrain from using such characters (or well use raw strings and forget about this problem).

What is the difference between using / and \\ in specifying folder location in python?

I am using python v3.6 on Windows 10. When specifying a string to represent a directory location, what is the difference between the 2 approaches below?
folder_location = 'C:\\Users\\username\\Dropbox\\Inv'
folder_location = 'C:/Users/username/Dropbox/Inv'
This is a follow-up question to another question I just posted. My problem was solved when I used \\ instead of /.
What is wrong with this selenium firefox profile to download file into customized folder?

On Unix systems, the folder separator is /, while on Windows systems, the separator is \. Unfortunately this \ is also an escape character in most programming languages and text based formats (including C, Python and many others). Strangely enough a / character is not allowed in windows paths.
So Python on windows is designed to accept both / and \ as folder separator when dealing with the filesystem, for convenience. But the \ must be escaped by another \ (unless of course you use raw strings like r'backslashes are now normal characters \\\ !')
Selenium, on the other hand, will write values into Firefox preferences, which, unlike Python, expects the appropriate kind of separator. That's why using forward slashes does not work in your example.

Windows uses by default backslashes as file/folder seperator the \\ is an escaped \. The POSIX compliant file/folder seperator / is also supported by the windows api. But the library you use (which is not recognizable in your example) need also support it.

The standard Windows path separator is backslash \. But it is used in string formatting so for example \n is end of line.
For the above reason you rather don't want to use backslash in you path as if the name of the folder will start with a letter corresponding to special characters you will run into troubles.
To use native backslash separator in windows you have two ways. Yo can use raw string and then all special characters are read literary. path = r"C:\user\myFolder" or escape backslach with escape character with turns out to be the backslash too path = "C:\\user\\myFolder".
But coming back to DOS it accepted forward slash in path string too
Python is able to accept both separators. It is advised to use native way of formatting on your system
If you want you script working on both systems try:
import os
if os.name == 'posix':
path = '/net/myFolder/'
else:
path = r'C:\Users\myFolder'

Windows inherited backslashes as a path separator from Microsoft DOS. DOS initially didn't support subdirectories and opted to use the (on US keyboards) easily typed slash / character for command line switches.
When they did introduce subdirectories in DOS 2, either slash / or backslash \ worked as a path separator, but to use slashes on the command line you had to reconfigure the switch character, a feature they later removed entirely.
Thus the command line for certain commands that look for switches without space in front (like dir/w) is the one place you can't use forward slashes (this has to do with the command line being passed as a single string, unlike POSIX which passes distinct arguments in a list). That, and poorly written code that tries things like splitting on backslash, not knowing that slash is also a path separator.
It's also sometimes complicated by either character having other meanings, such as \ being the escape character in string literals; that's why you use \\ unless you use a raw string r'foo\bar'.
The other path separator I know of is classic Mac OS, which uses colon :. Python handles these differences by including reasonable routines in os.path or pathlib.

Windows and Linux/macOS use different path separators - UNIX uses forward slashes (/) while Windows use back slashes (\).
You should never type your own separators, always use os.path.join or os.sep, which handle this for you based on the platform you're running on. Example:
import os
folder_location = os.path.join('C:\\', 'Users', 'username', 'Dropbox', 'Inv')
# or
folder_location = os.sep.join(['C:\\', 'Users', 'username', 'Dropbox', 'Inv']);
Also, you will need to manually escape the drive letter's trailing slash manually, as specified on the Python docs:
Note that on Windows, since there is a current directory for each drive, os.path.join("c:", "foo") represents a path relative to the current directory on drive C: (c:foo), not c:\foo.
Hard-coding a full path like this is usually useless, as C: will only work on Windows anyway. You will most likely want to use this later on using relative paths or paths that were fetched elsewhere and need to have segments added to them.

How can I create a file with `/` in its file name? [duplicate]

I know that this is not something that should ever be done, but is there a way to use the slash character that normally separates directories within a filename in Linux?

The answer is that you can't, unless your filesystem has a bug. Here's why:
There is a system call for renaming your file defined in fs/namei.c called renameat:
SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
int, newdfd, const char __user *, newname)
When the system call gets invoked, it does a path lookup (do_path_lookup) on the name. Keep tracing this, and we get to link_path_walk which has this:
static int link_path_walk(const char *name, struct nameidata *nd)
{
struct path next;
int err;
unsigned int lookup_flags = nd->flags;
while (*name=='/')
name++;
if (!*name)
return 0;
...
This code applies to any file system. What's this mean? It means that if you try to pass a parameter with an actual '/' character as the name of the file using traditional means, it will not do what you want. There is no way to escape the character. If a filesystem "supports" this, it's because they either:
Use a unicode character or something that looks like a slash but isn't.
They have a bug.
Furthermore, if you did go in and edit the bytes to add a slash character into a file name, bad things would happen. That's because you could never refer to this file by name :( since anytime you did, Linux would assume you were referring to a nonexistent directory. Using the 'rm *' technique would not work either, since bash simply expands that to the filename. Even rm -rf wouldn't work, since a simple strace reveals how things go on under the hood (shortened):
$ ls testdir
myfile2 out
$ strace -vf rm -rf testdir
...
unlinkat(3, "myfile2", 0) = 0
unlinkat(3, "out", 0) = 0
fcntl(3, F_GETFD) = 0x1 (flags FD_CLOEXEC)
close(3) = 0
unlinkat(AT_FDCWD, "testdir", AT_REMOVEDIR) = 0
...
Notice that these calls to unlinkat would fail because they need to refer to the files by name.

You could use a Unicode character that displays as / (for example the fraction slash), assuming your filesystem supports it.

It depends on what filesystem you are using. Of some of the more popular ones:
ext3: No
ext4: No
jfs: Yes
reiserfs: No
xfs: No

Only with an agreed-upon encoding. For example, you could agree that % will be encoded as %% and that %2F will mean a /. All the software that accessed this file would have to understand the encoding.

The short answer is: No, you can't. It's a necessary prohibition because of how the directory structure is defined.
And, as mentioned, you can display a unicode character that "looks like" a slash, but that's as far as you get.

In general it's a bad idea to try to use "bad" characters in a file name at all; even if you somehow manage it, it tends to make it hard to use the file later. The filesystem separator is flat-out not going to work at all, so you're going to need to pick an alternative method.
Have you considered URL-encoding the URL then using that as the filename? The result should be fine as a filename, and it's easy to reconstruct the name from the encoded version.
Another option is to create an index - create the output filename using whatever method you like - sequentially-numbered names, SHA1 hashes, whatever - then write a file with the generated filename/URL pair. You can save that into a hash and use it to do a URL-to-filename lookup or vice-versa with the reversed version of the hash, and you can write it out and reload it later if needed.

The short answer is: you must not. The long answer is, you probably can or it depends on where you are viewing it from and in which layer you are working with.
Since the question has Unix tag in it, I am going to answer for Unix.
As mentioned in other answers that, you must not use forward slashes in a filename.
However, in MacOS you can create a file with forward slashes / by:
# avoid doing it at all cost
touch 'foo:bar'
Now, when you see this filename from terminal you will see it as foo:bar
But, if you see it from finder: you will see finder converted it as foo/bar
Same thing can be done the other way round, if you create a file from finder with forward slashes in it like /foobar, there will be a conversion done in the background. As a result, you will see :foobar in terminal but the other way round when viewed from finder.
So, : is valid in the unix layer, but it is translated to or from / in the Mac layers like Finder window, GUI. : the colon is used as the separator in HFS paths and the slash / is used as the separator in POSIX paths
So there is a two-way translation happening, depending on which “layer” you are working with.
See more details here: https://apple.stackexchange.com/a/283095/323181

You can have a filename with a / in Linux and Unix. This is a very old question, but surprisingly nobody has said it in almost 10 years since the question was asked.
Every Unix and Linux system has the root directory named /. A directory is just a special kind of file. Symbolic links, character devices, etc are also special kinds of files. See here for an in depth discussion.
You can't create any other files with a /, but you certainly have one -- and a very important one at that.

How can I create files on Windows with embedded slashes, using Python?

After a half hour searching Google, I am surprised I cannot find any way to create a file on Windows with slashes in the name. The customer demands that file names have the following structure:
04/28/2012 04:07 PM 6,781 12Q1_C125_G_04-17.pdf
So far I haven't found any way to encode the slashes so they become part of the file name instead of the path.
Any Suggestions?

You can't.
The forward slash is one of the characters that are not allowed to be used in Windows file names, see
http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
The following fundamental rules enable applications to create and
process valid names for files and directories, regardless of the file
system:
Use a period to separate the base file name from the extension in the name of a directory or file.
Use a backslash (\) to separate the components of a path. The backslash divides the file name from the path to it, and one directory name from another directory name in a path. You cannot use a backslash in the name for the actual file or directory because it is a reserved character that separates the names into components.
Use a backslash as required as part of volume names, for example, the "C:\" in "C:\path\file" or the "\server\share" in
"\server\share\path\file" for Universal Naming Convention (UNC)
names. For more information about UNC names, see the Maximum Path
Length Limitation section.
Do not assume case sensitivity. For example, consider the names OSCAR, Oscar, and oscar to be the same, even though some file systems (such as a POSIX-compliant file system) may consider them as
different. Note that NTFS supports POSIX semantics for case
sensitivity but this is not the default behavior. For more
information, see CreateFile.
Volume designators (drive letters) are similarly case-insensitive. For example, "D:\" and "d:\" refer to the same volume.
Use any character in the current code page for a name, including Unicode characters and characters in the extended character set (128–255), except for the following:
The following reserved characters:
< (less than)
> (greater than)
: (colon)
" (double quote)
/ (forward slash)
\ (backslash)
| (vertical bar or pipe)
? (question mark)
* (asterisk)
Integer value zero, sometimes referred to as the ASCII NUL character.
Characters whose integer representations are in the range from 1 through 31, except for alternate data streams where these characters are allowed. For more information about file streams, see File
Streams.
Any other character that the target file system does not allow.

At least all windows installation i've seen won't let you create files with slashes in them.
Even if it were possible somehow, by doing deepshit magic, it will probably screw up almost all applications, including windows explorer.
you could abuse windows' unicode capabilities, though.
Creating a file with ∕ (this is not a forward slash, it is "division slash", see http://www.fileformat.info/info/unicode/char/2215/index.htm ) in it's name works just fine, for example.

Um... forward slash is not a legal character in a Windows file name?
http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx

How to make Python use a path that contains colons in it?

I have a program that includes an embedded Python 2.6 interpreter. When I invoke the interpreter, I call PySys_SetPath() to set the interpreter's import-path to the subdirectories installed next to my executable that contain my Python script files... like this:
PySys_SetPath("/path/to/my/program/scripts/type1:/path/to/my/program/scripts/type2");
(except that the path strings are dynamically generated based on the current location of my program's executable, not hard-coded as in the example above)
This works fine... except when the clever user decides to install my program underneath a folder that has a colon in its name. In that case, my PySys_SetPath() command ends up looking like this (note the presence of a folder named "path:to"):
PySys_SetPath("/path:to/my/program/scripts/type1:/path:to/my/program/scripts/type2");
... and this breaks all my Python scripts, because now Python looks for script files in "/path", and "to/my/program/scripts/type1" instead of in "/path:to/myprogram/scripts/type1", and so none of the import statements work.
My question is, is there any fix for this issue, other than telling the user to avoid colons in his folder names?
I looked at the makepathobject() function in Python/sysmodule.c, and it doesn't appear to support any kind of quoting or escaping to handle literal colons.... but maybe I am missing some nuance.

The problem you're running into is the PySys_SetPath function parses the string you pass using a colon as the delimiter. That parser sees each : character as delimiting a path, and there isn't a way around this (can't be escaped).
However, you can bypass this by creating a list of the individual paths (each of which may contain colons) and use PySys_SetObject to set the sys.path:
PyListObject *path;
path = (PyListObject *)PyList_New(0);
PyList_Append((PyObject *) path, PyString_FromString("foo:bar"));
PySys_SetObject("path", (PyObject *)path);
Now the interpreter will see "foo:bar" as a distinct component of the sys.path.

Supporting colons in a file path opens up a huge can of worms on multiple operating systems; it is not a valid path character on Windows or Mac OS X, for example, and it doesn't seem like a particularly reasonable thing to support in the context of a scripting environment either for exactly this reason. I'm actually a bit surprised that Linux allows colon filenames too, especially since : is a very common path separator character.
You might try escaping the colon out, i.e. converting /path:to/ to /path\:to/ and see if that works. Other than that, just tell the user to avoid using colons in their file names. They will run into all sorts of problems in quite a few different environments and it's a just plain bad idea.