Use [os.path.expandvars][1] to expand the environment variables in the string, for example:

    &gt;&gt;&gt; os.path.expandvars(&#39;$C/test/testing&#39;)
    &#39;/stackoverflow/test/testing&#39;


  [1]: http://docs.python.org/library/os.path.html#os.path.expandvars

In Python 3 you can do:

```
&#39;{VAR}&#39;.format(**os.environ))
```

for example

```
&gt;&gt;&gt; &#39;hello from {PWD}&#39;.format(**os.environ))
hello from /Users/william
```


I&#39;ve got a sproc (MSSQL 2k5) that will take a variable for a LIKE claus like so:

    DECLARE @SearchLetter2 char(1)
    SET @SearchLetter = &#39;t&#39;
    SET @SearchLetter2 = @SearchLetter + &#39;%&#39;
    SELECT *
        FROM BrandNames 
        WHERE [Name] LIKE @SearchLetter2 and IsVisible = 1 
        --WHERE [Name] LIKE &#39;t%&#39; and IsVisible = 1 
        ORDER BY [Name]

Unfortunately, the line currently running throws a syntax error, while the commented where clause runs just fine.  Can anyone help me get the un-commented line working?

Using variable in SQL LIKE statement

(Note: I realize this is close to https://stackoverflow.com/questions/186392/how-do-you-document-your-database-structure , but I don&#39;t think it&#39;s identical.)

I&#39;ve started work at a place with a database with literally hundreds of tables and views, all with cryptic names with very few vowels, and no documentation.  They also don&#39;t allow gratuitous changes to the database schema, nor can I touch any database except the test one on my own machine (which gets blown away and recreated regularly), so I can&#39;t add comments that would help anybody.  

I tried using &quot;Toad&quot; to create an ER diagram, but after leaving it running for 48 hours straight it still hadn&#39;t produced anything visible and I needed my computer back.  I was talking to some other recent hires and we all suggested that whenever we&#39;ve puzzled out what a particular table or what some of its columns means, we should update it in the developers wiki.

So what&#39;s a good way to do this?  Just list tables/views and their columns and fill them in as we go?  The basic tools I&#39;ve got to hand are Toad, Oracle&#39;s &quot;SQL Developer&quot;, MS Office, and Visio.

How to document a database

I have a string representing a path.  Because this application is used on Windows, OSX and Linux, we&#39;ve defined environment variables to properly map volumes from the different file systems.  The result is:

    &quot;$C/test/testing&quot;

What I want to do is evaluate the environment variables in the string so that they&#39;re replaced by their respective volume names.  Is there a specific command I&#39;m missing, or do I have to take `os.environ.keys()` and manually replace the strings?

How to evaluate environment variables into a string in Python?

I have a string representing a path. Because this application is used on Windows, OSX and Linux, we've defined environment variables to properly map volumes from the different file systems. The result is:
<pre><code class="hljs language-bash">"$C/test/testing"
</code></pre>
What I want to do is evaluate the environment variables in the string so that they're replaced by their respective volume names. Is there a specific command I'm missing, or do I have to take <code>os.environ.keys()</code> and manually replace the strings?

How do you gracefully handle failed future feature imports? If a user is running using Python 2.5 and the first statement in my module is:

    from __future__ import print_function

Compiling this module for Python 2.5 will fail with a:

      File &quot;__init__.py&quot;, line 1
        from __future__ import print_function
    SyntaxError: future feature print_function is not defined

I&#39;d like to inform the user that they need to rerun the program with Python &gt;= 2.6 and maybe provide some instructions on how to do so. However, to quote [PEP 236][1]:

&gt; The only lines that can appear before
&gt; a future_statement are:
&gt; 
&gt; + The module docstring (if any).
&gt; + Comments.
&gt; + Blank lines.
&gt; + Other future_statements.

So I can&#39;t do something like:

    import __future__
    
    if hasattr(__future__, &#39;print_function&#39;):
        from __future__ import print_function
    else:
        raise ImportError(&#39;Python &gt;= 2.6 is required&#39;)

Because it yields:

      File &quot;__init__.py&quot;, line 4
        from __future__ import print_function
    SyntaxError: from __future__ imports must occur at the beginning of the file

This snippet from the PEP seems to give hope of doing it inline:

&gt; Q:  I want to wrap future_statements
&gt; in try/except blocks, so I can use
&gt; different code depending on which
&gt; version of Python I&#39;m running.  Why
&gt; can&#39;t I?
&gt; 
&gt; A:  Sorry!  try/except is a runtime
&gt; feature; future_statements are
&gt; primarily compile-time gimmicks, and
&gt; your try/except happens long after the
&gt; compiler is done.  That is, by the
&gt; time you do try/except, the semantics
&gt; in effect for the module are already a
&gt; done deal.  Since the try/except
&gt; wouldn&#39;t accomplish what it *looks*
&gt; like it should accomplish, it&#39;s simply
&gt; not allowed.  We also want to keep
&gt; these special statements very easy to
&gt; find and to recognize.
&gt; 
&gt; Note that you *can* import \_\_future\_\_
&gt; directly, and use the information in
&gt; it, along with sys.version_info, to
&gt; figure out where the release you&#39;re
&gt; running under stands in relation to a
&gt; given feature&#39;s status.

Ideas?

  [1]: http://www.python.org/dev/peps/pep-0236/

How to gracefully deal with failed future feature (__future__) imports due to old interpreter version?

For example I can point the `url &#39;^/accounts/password/reset/$&#39;` to `django.contrib.auth.views.password_reset` with my template filename in the context but I think need to send more context details.

I need to  know exactly what context to add for each of the password reset and change views.


How do I use the built in password reset/change views with my own templates

When writing custom classes it is often important to allow equivalence by means of the `==` and `!=` operators. In Python, this is made possible by implementing the `__eq__` and `__ne__` special methods, respectively. The easiest way I&#39;ve found to do this is the following method:

    class Foo:
        def __init__(self, item):
            self.item = item

        def __eq__(self, other):
            if isinstance(other, self.__class__):
                return self.__dict__ == other.__dict__
            else:
                return False

        def __ne__(self, other):
            return not self.__eq__(other)

Do you know of more elegant means of doing this? Do you know of any particular disadvantages to using the above method of comparing `__dict__`s?

**Note**: A bit of clarification--when `__eq__` and `__ne__` are undefined, you&#39;ll find this behavior:

    &gt;&gt;&gt; a = Foo(1)
    &gt;&gt;&gt; b = Foo(1)
    &gt;&gt;&gt; a is b
    False
    &gt;&gt;&gt; a == b
    False

That is, `a == b` evaluates to `False` because it really runs `a is b`, a test of identity (i.e., &quot;Is `a` the same object as `b`?&quot;).

When `__eq__` and `__ne__` are defined, you&#39;ll find this behavior (which is the one we&#39;re after):

    &gt;&gt;&gt; a = Foo(1)
    &gt;&gt;&gt; b = Foo(1)
    &gt;&gt;&gt; a is b
    False
    &gt;&gt;&gt; a == b
    True

Elegant ways to support equivalence (&quot;equality&quot;) in Python classes

For example, files, in Python, are iterable - they iterate over the lines in the file. I want to count the number of lines. 

One quick way is to do this:

    lines = len(list(open(fname)))

However, this loads the whole file into memory (at once). This rather defeats the purpose of an iterator (which only needs to keep the current line in memory).

This doesn&#39;t work:

    lines = len(line for line in open(fname))

as generators don&#39;t have a length.

Is there any way to do this short of defining a count function?

    def count(i):
        c = 0
        for el in i: c += 1
        return c

To clarify, I understand that the whole file will have to be read! I just don&#39;t want it in memory all at once

Is there any built-in way to get the length of an iterable in python?

There is a JavaScript parser at least in C and Java (Mozilla), in JavaScript (Mozilla again) and Ruby. Is there any currently out there for Python?

I don&#39;t need a JavaScript interpreter, per se, just a parser that&#39;s up to ECMA-262 standards.

A quick google search revealed no immediate answers, so I&#39;m asking the SO community.

JavaScript parser in Python

I&#39;m thinking about developing my own PHP based gallery for storing lots of pictures, maybe in the tens of thousands.

At the database I&#39;ll point to the url of the image, but here&#39;s the problem: I know is impractical to have all of them sitting at the same directory in the server as it would slow access to a crawl, so, how would you store all of them? Some kind of tree based on the name of the jpeg/png?

What rules to partition the images would you recommend me?

(It will focused for using in cheapo dot coms, so no mangling with the server is possible)

Storing a large number of images

Does it matter how many files I keep in a single directory? If so, how many files in a directory is too many, and what are the impacts of having too many files? (This is on a Linux server.)

Background: I have a photo album website, and every image uploaded is renamed to an 8-hex-digit id (say, a58f375c.jpg).  This is to avoid filename conflicts (if lots of &quot;IMG0001.JPG&quot; files are uploaded, for example).  The original filename and any useful metadata is stored in a database.  Right now, I have somewhere around 1500 files in the images directory.  This makes listing the files in the directory (through FTP or SSH client) take a few seconds.  But I can&#39;t see that it has any effect other than that.  In particular, there doesn&#39;t seem to be any impact on how quickly an image file is served to the user.

I&#39;ve thought about reducing the number of images by making 16 subdirectories: 0-9 and a-f.  Then I&#39;d move the images into the subdirectories based on what the first hex digit of the filename was.  But I&#39;m not sure that there&#39;s any reason to do so except for the occasional listing of the directory through FTP/SSH.

How many files can I put in a directory?

I need to determine if a user-supplied string is a valid file path (i.e., if `createNewFile()` will succeed or throw an Exception) but I don&#39;t want to bloat the file system with useless files, created just for validation purposes.

Is there a way to determine if the string I have is a valid file path without attempting to create the file?

I know the definition of &quot;valid file path&quot; varies depending on the OS, but I was wondering if there was any quick way of accepting `C:/foo` or `/foo` and rejecting `banana`.

A possible approach may be attempting to create the file and eventually deleting it if the creation succeeded, but I hope there is a more elegant way of achieving the same result.


Is there a way in Java to determine if a path is valid without attempting to create a file?

How to get directory size in PHP

I&#39;m looking for a cross-platform file monitoring python package? I know it is possible to monitor files on windows using pywin32, and there are packages working on Linux/Unix but does anyone know about a cross-platform one?

Monitoring contents of files/directories?

How do I set Java&#39;s min and max heap size through environment variables?

I know that the heap sizes can be set when launching java, but I would like to have this adjusted through environment variables on my server.

How do I set Java&#39;s min and max heap size through environment variables?

I came across a reference to it recently on [proggit](http://www.reddit.com/r/programming/comments/7o8d9/tcmalloca_faster_malloc_than_glibcs_open_sourced/c06wjka) and (as of now) it is not explained.

I suspect [this](https://stackoverflow.com/questions/335108/hide-symbols-in-shared-object-from-ld#335253) might be it, but I don&#39;t know for sure.

What is the LD_PRELOAD trick?

How can I get the System Variable value which is present in 

    MyComputer -&gt; Properties -&gt; Advanced -&gt; Environment Variables -&gt; System Variables

in Java?

*Edit*

I have used `System.getenv()` method.

It is printing value if I give 

    System.out.println(System.getenv(&quot;JAVA_HOME&quot;));

and it is showing `null` value if I try the same for system variable created by me 

    System.out.println(System.getenv(&quot;DBE&quot;));

How can I get System variable value in Java?

If I type into a terminal,

    export DISPLAY=:0.0

... where is the shell storing that environment variable?

I&#39;m using Ubuntu 8.10. I&#39;ve looked in the files ~/.profile and /etc/profile and can find no trace of DISPLAY.

Linux: where are environment variables stored?

I&#39;d like gcc to include files from `$HOME/include` in addition to the usual include directories, but there doesn&#39;t seem to be an analogue to `$LD_LIBRARY_PATH`.

I know I can just add the include directory at command line when compiling (or in the makefile), but I&#39;d really like a universal approach here, as in the library case.

Content Type	Original Author	Original Content on Stackoverflow
Question	Soviut	View Question on Stackoverflow
Solution 1 - Python	jblocksom	View Answer on Stackoverflow
Solution 2 - Python	william_grisaitis	View Answer on Stackoverflow

How to evaluate environment variables into a string in Python?

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

How to document a database

Using variable in SQL LIKE statement

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