Use [`datetime.timedelta()`][1]

    &gt;&gt;&gt; from datetime import date, timedelta
    &gt;&gt;&gt; yesterday = date.today() - timedelta(days=1)
    &gt;&gt;&gt; yesterday.strftime(&#39;%m%d%y&#39;)
    &#39;110909&#39;


  [1]: https://docs.python.org/library/datetime.html#timedelta-objects

    from datetime import datetime, timedelta
    
    yesterday = datetime.now() - timedelta(days=1)
    yesterday.strftime(&#39;%m%d%y&#39;)

This should do what you want:

    import datetime
    yesterday = datetime.datetime.now() - datetime.timedelta(days = 1)
    print yesterday.strftime(&quot;%m%d%y&quot;)



all answers are correct, but I want to mention that time delta **accepts negative arguments**.    


    &gt;&gt;&gt; from datetime import date, timedelta
    &gt;&gt;&gt; yesterday = date.today() + timedelta(days=-1)
    &gt;&gt;&gt; print(yesterday.strftime(&#39;%m%d%y&#39;)) #for python2 remove parentheses 

Could I just make this somewhat more international and format the date according to the international standard and not in the weird month-day-year, that is common in the US?

    from datetime import datetime, timedelta

    yesterday = datetime.now() - timedelta(days=1)
    yesterday.strftime(&#39;%Y-%m-%d&#39;)

To expand on the answer given by [Chris](https://stackoverflow.com/a/7917292/7262144)

	
if you want to store the date in a variable in a specific format, this is the shortest and most effective way as far as I know

    &gt;&gt;&gt; from datetime import date, timedelta                   
    &gt;&gt;&gt; yesterday = (date.today() - timedelta(days=1)).strftime(&#39;%m%d%y&#39;)
    &gt;&gt;&gt; yesterday
    &#39;020817&#39;
If you want it as an integer (which can be useful)

    &gt;&gt;&gt; yesterday = int((date.today() - timedelta(days=1)).strftime(&#39;%m%d%y&#39;))
    &gt;&gt;&gt; yesterday
    20817

I&#39;m experimenting with building an entire web application using Node.js. Is there a template engine similar to (for example) the Django template engine or the like that at least allows you to extend base templates?



Is there a template engine for Node.js?

I would like to know a list of the most common application/websites/solutions where Erlang is used, **successfully or not**.

Explaining why it is used into a specific solution instead of others programming languages would be very much appreciated, too.

Listing BAD Erlang case studies (cases in which Erlang is misused) it would be interesting, as well.


Where is Erlang used and why?

I need to find &quot;yesterday&#39;s&quot; date in this format `MMDDYY` in Python.

So for instance, today&#39;s date would be represented like this:
111009

I can easily do this for today but I have trouble doing it automatically for &quot;yesterday&quot;.

Formatting &quot;yesterday&#39;s&quot; date in python

I need to find "yesterday's" date in this format <code>MMDDYY</code> in Python.
So for instance, today's date would be represented like this:
111009
I can easily do this for today but I have trouble doing it automatically for "yesterday".

How do I get the number of elements in the list `items`?

    items = [&quot;apple&quot;, &quot;orange&quot;, &quot;banana&quot;]

    # There are 3 items.



How do I get the number of elements in a list in Python?

I get some error that I can&#39;t figure out. Any clue what is wrong with my sample code?

    class B:
        def meth(self, arg):
            print arg
    
    class C(B):
        def meth(self, arg):
            super(C, self).meth(arg)
    
    print C().meth(1)

I got the sample test code from help of &#39;super&#39; built-in method. 

Here is the error:

    Traceback (most recent call last):
      File &quot;./test.py&quot;, line 10, in ?
        print C().meth(1)
      File &quot;./test.py&quot;, line 8, in meth
        super(C, self).meth(arg)
    TypeError: super() argument 1 must be type, not classobj

FYI, here is the help(super) from python itself:

    Help on class super in module __builtin__:
    
    class super(object)
     |  super(type) -&gt; unbound super object
     |  super(type, obj) -&gt; bound super object; requires isinstance(obj, type)
     |  super(type, type2) -&gt; bound super object; requires issubclass(type2, type)
     |  Typical use to call a cooperative superclass method:
     |  class C(B):
     |      def meth(self, arg):
     |          super(C, self).meth(arg)
     |



super() fails with error: TypeError &quot;argument 1 must be type, not classobj&quot; when parent does not inherit from object

I can write something myself by finding zero-crossings of the first derivative or something, but it seems like a common-enough function to be included in standard libraries.  Anyone know of one?

My particular application is a 2D array, but usually it would be used for finding peaks in FFTs, etc.

Specifically, in these kinds of problems, there are multiple strong peaks, and then lots of smaller &quot;peaks&quot; that are just caused by noise that should be ignored.  These are just examples; not my actual data:

1-dimensional peaks:

[![FFT output with peaks][2]][2]

2-dimensional peaks:

![Radon transform output with circled peak][3]

The peak-finding algorithm would find the location of these peaks (not just their values), and ideally would find the true inter-sample peak, not just the index with maximum value, probably using [quadratic interpolation][4] or something.

Typically you only care about a few strong peaks, so they&#39;d either be chosen because they&#39;re above a certain threshold, or because they&#39;re the first *n* peaks of an ordered list, ranked by amplitude.

As I said, I know how to write something like this myself.  I&#39;m just asking if there&#39;s a pre-existing function or package that&#39;s known to work well.

**Update:**

I [translated a MATLAB script][5] and it works decently for the 1-D case, but could be better.

**Updated update:**

sixtenbe [created a better version][7] for the 1-D case.


  [1]: http://i.stack.imgur.com/F5e8F.png
  [2]: http://i.stack.imgur.com/eJvFQ.jpg
  [3]: http://i.stack.imgur.com/MBh1r.png
  [4]: https://ccrma.stanford.edu/~jos/sasp/Quadratic_Peak_Interpolation.html
  [5]: http://gist.github.com/250860
  [7]: https://gist.github.com/1178136

Peak-finding algorithm for Python/SciPy

I want to write a `cmp`-like function that compares two version numbers and returns `-1`, `0`, or `1` based on their compared values.

 - Return `-1` if version A is older than version B
 - Return `0` if versions A and B are equivalent
 - Return `1` if version A is newer than version B

Each subsection is supposed to be interpreted as a number, therefore 1.10 &gt; 1.1. 

Desired function outputs are

    mycmp(&#39;1.0&#39;, &#39;1&#39;) == 0
    mycmp(&#39;1.0.0&#39;, &#39;1&#39;) == 0
    mycmp(&#39;1&#39;, &#39;1.0.0.1&#39;) == -1
    mycmp(&#39;12.10&#39;, &#39;11.0.0.0.0&#39;) == 1
    ...

And here is my implementation, open for improvement:


    def mycmp(version1, version2):
        parts1 = [int(x) for x in version1.split(&#39;.&#39;)]
        parts2 = [int(x) for x in version2.split(&#39;.&#39;)]

        # fill up the shorter version with zeros ...
        lendiff = len(parts1) - len(parts2)
        if lendiff &gt; 0:
            parts2.extend([0] * lendiff)
        elif lendiff &lt; 0:
            parts1.extend([0] * (-lendiff))
    
        for i, p in enumerate(parts1):
            ret = cmp(p, parts2[i])
            if ret: return ret
        return 0

I&#39;m using Python 2.4.5 btw. (installed at my working place ...).

Here&#39;s a small &#39;test suite&#39; you can use

    assert mycmp(&#39;1&#39;, &#39;2&#39;) == -1
    assert mycmp(&#39;2&#39;, &#39;1&#39;) == 1
    assert mycmp(&#39;1&#39;, &#39;1&#39;) == 0
    assert mycmp(&#39;1.0&#39;, &#39;1&#39;) == 0
    assert mycmp(&#39;1&#39;, &#39;1.000&#39;) == 0
    assert mycmp(&#39;12.01&#39;, &#39;12.1&#39;) == 0
    assert mycmp(&#39;13.0.1&#39;, &#39;13.00.02&#39;) == -1
    assert mycmp(&#39;1.1.1.1&#39;, &#39;1.1.1.1&#39;) == 0
    assert mycmp(&#39;1.1.1.2&#39;, &#39;1.1.1.1&#39;) == 1
    assert mycmp(&#39;1.1.3&#39;, &#39;1.1.3.000&#39;) == 0
    assert mycmp(&#39;3.1.1.0&#39;, &#39;3.1.2.10&#39;) == -1
    assert mycmp(&#39;1.1&#39;, &#39;1.10&#39;) == -1




Version number comparison in Python

I want to create a non-thread-safe chunk of code for experimentation, and those are the functions that 2 threads are going to call.

    c = 0
    
    def increment():
      c += 1
    
    def decrement():
      c -= 1

Is this code thread safe?

If not, may I understand why it is not thread safe, and what kind of statements usually lead to non-thread-safe operations.

If it is thread-safe, how can I make it explicitly non-thread-safe?

Is the += operator thread-safe in Python?

Oracle&#39;s table server offers a built-in function, `TRUNC(timestamp,&#39;DY&#39;)`. This function converts any timestamp to midnight on the previous Sunday. What&#39;s the best way to do this in MySQL?

Oracle also offers `TRUNC(timestamp,&#39;MM&#39;)` to convert a timestamp to midnight on the first day of the month in which it occurs. In MySQL, this one is straightforward:

    TIMESTAMP(DATE_FORMAT(timestamp, &#39;%Y-%m-01&#39;))

But this `DATE_FORMAT` trick won&#39;t work for weeks. I&#39;m aware of the `WEEK(timestamp)` function, but I really don&#39;t want week number within the year; this stuff is for multiyear work.


How to group by week in MySQL?

For Django 1.1.

I have this in my models.py:

    class User(models.Model):
        created = models.DateTimeField(auto_now_add=True)
        modified = models.DateTimeField(auto_now=True)

When updating a row I get:

    [Sun Nov 15 02:18:12 2009] [error] /home/ptarjan/projects/twitter-meme/django/db/backends/mysql/base.py:84: Warning: Column &#39;created&#39; cannot be null
    [Sun Nov 15 02:18:12 2009] [error]   return self.cursor.execute(query, args)

The relevant part of my database is:

      `created` datetime NOT NULL,
      `modified` datetime NOT NULL,

Is this cause for concern?

Side question: in my admin tool, those two fields aren&#39;t showing up. Is that expected?


Django auto_now and auto_now_add

I&#39;m writing a bit of logic that requires treating null dates as meaning forever in the future (the date in question is an expiration date, which may or may not exist). Instead of putting in special cases for a null date throughout the code, I want to just convert null into the maximum possible Date. I don&#39;t see any obvious ways to get such a value without hard coding it. What&#39;s the best way to get the maximum value of whatever Date implementation is being used?

Best way to get maximum Date value in java?

I have a column of type &quot;datetime&quot; with values like 2009-10-20 10:00:00

I would like to extract date from datetime and write a query like:

    SELECT * FROM 
    data 
    WHERE datetime = &#39;2009-10-20&#39; 
    ORDER BY datetime DESC

Is the following the best way to do it?

    SELECT * FROM 
    data 
    WHERE datetime BETWEEN(&#39;2009-10-20 00:00:00&#39; AND &#39;2009-10-20 23:59:59&#39;)
    ORDER BY datetime DESC

This however returns an empty resultset. Any suggestions?



How to select date from datetime column?

*Why* can&#39;t it parse this:

    DateTime.Parse(&quot;Tue, 1 Jan 2008 00:00:00 UTC&quot;)

Why can&#39;t DateTime.Parse parse UTC date

How do I disable past dates on jQuery datepicker? I looked for options but don&#39;t seem to find anything that indicates the ability to disable past dates. 

UPDATE: Thanks yall for the quick response. I tried that with no luck. Days were still not grayed out as I expected and still accept the selected past date. 

I tried this:

    $(&#39;#datepicker&#39;).datepicker({ minDate: &#39;0&#39; });

Doesn&#39;t work.

I tried this:

    $(&#39;#datepicker&#39;).datepicker({ minDate: new Date() });

Still doesn&#39;t work either. 

It displays the calendar widget just fine. It just won&#39;t gray out or prevent input of past days. I&#39;ve attempted the minDate and maxDate in the past with no luck so I figured it must not be them. 




jQuery datepicker to prevent past date

How would you check time difference from two text-boxes in Javascript?

Check time difference in Javascript

How do I exclude values in a `DateTime` column that are Saturdays or Sundays?

For example, given the following data:

    date_created
    &#39;2009-11-26 09:00:00&#39;  -- Thursday
    &#39;2009-11-27 09:00:00&#39;  -- Friday
    &#39;2009-11-28 09:00:00&#39;  -- Saturday
    &#39;2009-11-29 09:00:00&#39;  -- Sunday
    &#39;2009-11-30 09:00:00&#39;  -- Monday

this is the result I&#39;m looking for:

    date_created
    &#39;2009-11-26 09:00:00&#39;  -- Thursday
    &#39;2009-11-27 09:00:00&#39;  -- Friday
    &#39;2009-11-30 09:00:00&#39;  -- Monday

Thanks!

How do I exclude Weekend days in a SQL Server query?

How would I get a UNIX timestamp (number of seconds since 1970 GMT) from a Date object in a Rails app?

I know `Time#to_i` returns a timestamp, but doing `Date#to_time` and then getting the timestamp results in something that&#39;s off by about a month (not sure why...). 

Any help is appreciated, thanks!

Edit: OK, I think I figured it out- I was processing a date several times in a loop, and each time the date was moved a little because of a time zone mismatch, ultimately leading to my timestamp being a month off. Still, I&#39;d be interested in knowing if there&#39;s any way to do this without relying on `Date#to_time`.

Content Type	Original Author	Original Content on Stackoverflow
Question	y2k	View Question on Stackoverflow
Solution 1 - Python	Jarret Hardie	View Answer on Stackoverflow
Solution 2 - Python	Nadia Alramli	View Answer on Stackoverflow
Solution 3 - Python	Stef	View Answer on Stackoverflow
Solution 4 - Python	Iman Mirzadeh	View Answer on Stackoverflow
Solution 5 - Python	Arvid Bäärnhielm	View Answer on Stackoverflow
Solution 6 - Python	Pär Berge	View Answer on Stackoverflow

Formatting "yesterday's" date in python

Python Problem Overview

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Where is Erlang used and why?

Is there a template engine for Node.js?

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