    lst1, lst2 = zip(*zipped_list)

should give you the unzipped list.

`*zipped_list` unpacks the zipped_list object. it then passes all the tuples from the zipped_list object to zip, which just packs them back up as they were when you passed them in.

so if:

    a = [1,2,3]
    b = [4,5,6]

then `zipped_list = zip(a,b)` gives you:

    [(1,4), (2,5), (3,6)]

and `*zipped_list` gives you back

    (1,4), (2,5), (3,6)

zipping that with `zip(*zipped_list)` gives you back the two collections:

    [(1, 2, 3), (4, 5, 6)]

So here&#39;s what I want to do on my _MySQL_ database.

I would like to do:

    SELECT *
        FROM itemsOrdered
        WHERE purchaseOrder_ID = &#39;@purchaseOrdered_ID&#39;
            AND status = &#39;PENDING&#39;

If that would not return any rows, which is possible through `if(dr.HasRows == false)`, I would now create an `UPDATE` in the `purchaseOrder` database:

    UPDATE purchaseOrder
        SET purchaseOrder_status = &#39;COMPLETED&#39;
        WHERE purchaseOrder_ID = &#39;@purchaseOrder_ID&#39;

How would I be able to make this process a little shorter?


How do I put an &#39;if clause&#39; in an SQL string?



    var err1 = Error(&#39;message&#39;);
    var err2 = new Error(&#39;message&#39;);


What&#39;s the difference? Looking at them in the chrome console, they look identical. Same properties on the object and the same `__proto__` chain. Almost seems like `Error` acts like a factory.

Which one is correct and why?

throw Error(&#39;msg&#39;) vs throw new Error(&#39;msg&#39;)

&gt; **Possible Duplicate:**  
&gt; [A Transpose/Unzip Function in Python](https://stackoverflow.com/questions/19339/a-transpose-unzip-function-in-python)  

&lt;!-- End of automatically inserted text --&gt;

I&#39;ve used the zip() function from the numpy library to sort tuples and now I have a list containing all the tuples. I had since modified that list and now I would like to restore the tuples so I can use my data. How can I do this?

What is the inverse function of zip in python?

> Possible Duplicate: 
> <a href="https://stackoverflow.com/questions/19339/a-transpose-unzip-function-in-python" target="_blank" rel="noopener noreferrer">A Transpose/Unzip Function in Python</a>

I've used the zip() function from the numpy library to sort tuples and now I have a list containing all the tuples. I had since modified that list and now I would like to restore the tuples so I can use my data. How can I do this?

I have a couple of problems to solve for an assignment, and am a bit stuck.
The question is to write a program that gets the user to input an odd number (check it&#39;s odd), then print an upside down pyramid of stars based on the size of the input.

For example, if you enter 5, it comes up with

    *****
     ***
      *
My problem is therefore two-fold.

1) How do I check if it&#39;s even or odd? I tried `if number/2 == int` in the hope that it might do something, and the internet tells me to do `if number%2==0`, but that doesn&#39;t work.

2) How do I change the asterisks in the middle of each line?

Any help with either problem is greatly appreciated.

Checking odd/even numbers and changing outputs on number size

I have two DataFrames which I want to merge based on a column. However, due to alternate spellings, different number of spaces, absence/presence of diacritical marks, I would like to be able to merge as long as they are similar to one another.

Any similarity algorithm will do (soundex, Levenshtein, difflib&#39;s). 

Say one DataFrame has the following data:

    df1 = DataFrame([[1],[2],[3],[4],[5]], index=[&#39;one&#39;,&#39;two&#39;,&#39;three&#39;,&#39;four&#39;,&#39;five&#39;], columns=[&#39;number&#39;])

           number
    one         1
    two         2
    three       3
    four        4
    five        5
    
    df2 = DataFrame([[&#39;a&#39;],[&#39;b&#39;],[&#39;c&#39;],[&#39;d&#39;],[&#39;e&#39;]], index=[&#39;one&#39;,&#39;too&#39;,&#39;three&#39;,&#39;fours&#39;,&#39;five&#39;], columns=[&#39;letter&#39;])

          letter
    one        a
    too        b
    three      c
    fours      d
    five       e

Then I want to get the resulting DataFrame

           number letter
    one         1      a
    two         2      b
    three       3      c
    four        4      d
    five        5      e



is it possible to do fuzzy match merge with python pandas?

`filter`, `map`, and `reduce` work perfectly in Python 2. Here is an example:

    &gt;&gt;&gt; def f(x):
            return x % 2 != 0 and x % 3 != 0
    &gt;&gt;&gt; filter(f, range(2, 25))
    [5, 7, 11, 13, 17, 19, 23]

    &gt;&gt;&gt; def cube(x):
            return x*x*x
    &gt;&gt;&gt; map(cube, range(1, 11))
    [1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]

    &gt;&gt;&gt; def add(x,y):
            return x+y
    &gt;&gt;&gt; reduce(add, range(1, 11))
    55

But in Python 3, I receive the following outputs:

    &gt;&gt;&gt; filter(f, range(2, 25))
    &lt;filter object at 0x0000000002C14908&gt;

    &gt;&gt;&gt; map(cube, range(1, 11))
    &lt;map object at 0x0000000002C82B70&gt;

    &gt;&gt;&gt; reduce(add, range(1, 11))
    Traceback (most recent call last):
      File &quot;&lt;pyshell#8&gt;&quot;, line 1, in &lt;module&gt;
        reduce(add, range(1, 11))
    NameError: name &#39;reduce&#39; is not defined

I would appreciate if someone could explain to me why this is.

Screenshot of code for further clarity:

[![IDLE sessions of Python 2 and 3 side-by-side](http://i.imgur.com/WekeD.png)](http://i.imgur.com/WekeD.png)

How to use filter, map, and reduce in Python 3

How can I make a class or method abstract in Python?

I tried redefining `__new__()` like so:

    class F:
        def __new__(cls):
            raise Exception(&quot;Unable to create an instance of abstract class %s&quot; %cls)

but now if I create a class `G` that inherits from `F` like so:

    class G(F):
        pass

then I can&#39;t instantiate `G` either, since it calls its super class&#39;s `__new__` method.

Is there a better way to define an abstract class?

Is it possible to make abstract classes in Python?

I have an array of datetime64 type:

    dates = np.datetime64([&#39;2010-10-17&#39;, &#39;2011-05-13&#39;, &quot;2012-01-15&quot;])
Is there a better way than looping through each element just to get np.array of years:

    years = f(dates)
    #output:
    array([2010, 2011, 2012], dtype=int8) #or dtype = string

I&#39;m using stable numpy version 1.6.2.

Get year, month or day from numpy datetime64

I&#39;m trying to take a file that looks like this:
```none
AAA x 111
AAB x 111
AAA x 112
AAC x 123
...
```
And use a dictionary to so that the output looks like this

    {AAA: [&#39;111&#39;, &#39;112&#39;], AAB: [&#39;111&#39;], AAC: [123], ...}

This is what I&#39;ve tried

    file = open(&quot;filename.txt&quot;, &quot;r&quot;) 
    readline = file.readline().rstrip()
    while readline!= &quot;&quot;:
        list = []
        list = readline.split(&quot; &quot;)
        j = list.index(&quot;x&quot;)
        k = list[0:j]
        v = list[j + 1:]
        d = {}
        if k not in d == False:
            d[k] = []
        d[k].append(v)
        readline = file.readline().rstrip()

I keep getting a `TypeError: unhashable type: &#39;list&#39;`. I know that keys in a dictionary can&#39;t be lists but I&#39;m trying to make my value into a list not the key. I&#39;m wondering if I made a mistake somewhere.


How to overcome TypeError: unhashable type: &#39;list&#39;

### Background:

Example list: `mylist = [&#39;abc123&#39;, &#39;def456&#39;, &#39;ghi789&#39;]`

I want to retrieve an element if there&#39;s a match for a substring, like `abc`

### Code:

    sub = &#39;abc&#39;
    print any(sub in mystring for mystring in mylist)

above prints `True` if any of the elements in the list contain the pattern.

I would like to print the element which matches the substring. So if I&#39;m checking `&#39;abc&#39;` I only want to print `&#39;abc123&#39;` from list.


Finding a substring within a list in Python

I need to write a function that takes
a **list** of numbers and **multiplies** them together. Example:
`[1,2,3,4,5,6]` will give me `1*2*3*4*5*6`. I could really use your help.



How can I multiply all items in a list together with Python?

I am currently working my way through the [Learn you a Haskell](http://www.learnyouahaskell.com/for-a-few-monads-more) book online, and have come to a chapter where the author is explaining that some list concatenations can be inefficient: For example

    ((((a ++ b) ++ c) ++ d) ++ e) ++ f

is supposedly inefficient. The solution the author comes up with is to use &#39;difference lists&#39; defined as 

    newtype DiffList a = DiffList {getDiffList :: [a] -&gt; [a] }

    instance Monoid (DiffList a) where
        mempty = DiffList (\xs -&gt; [] ++ xs)
        (DiffList f) `mappend` (DiffList g) = DiffList (\xs -&gt; f (g xs))

I am struggling to understand why `DiffList` is more computationally efficient than a simple concatenation in some cases. Could someone explain to me in simple terms why the above example is so inefficient, and in what way the `DiffList` solves this problem?


Why are difference lists more efficient than regular concatenation in Haskell?

What is the quickest and cleanest way to convert an `integer` into a `list`? 
  
For example, change `132` into `[1,3,2]` and `23` into `[2,3]`. I have a variable which is an `int`, and I want to be able to compare the individual digits so I thought making it into a list would be best, since I can just do `int(number[0])`, `int(number[1])` to easily convert the list element back into int for digit operations.

Converting integer to digit list

How do I convert a `numpy.datetime64` object to a `datetime.datetime` (or `Timestamp`)?

In the following code, I create a datetime, timestamp and datetime64 objects.

    import datetime
    import numpy as np
    import pandas as pd
    dt = datetime.datetime(2012, 5, 1)
    # A strange way to extract a Timestamp object, there&#39;s surely a better way?
    ts = pd.DatetimeIndex([dt])[0]
    dt64 = np.datetime64(dt)

    In [7]: dt
    Out[7]: datetime.datetime(2012, 5, 1, 0, 0)
   
    In [8]: ts
    Out[8]: &lt;Timestamp: 2012-05-01 00:00:00&gt;

    In [9]: dt64
    Out[9]: numpy.datetime64(&#39;2012-05-01T01:00:00.000000+0100&#39;)

*Note: it&#39;s easy to get the datetime from the Timestamp:*

    In [10]: ts.to_datetime()
    Out[10]: datetime.datetime(2012, 5, 1, 0, 0)

But how do we extract the `datetime` or `Timestamp` from a `numpy.datetime64` (`dt64`)?

.

Update: a somewhat nasty example in my dataset (perhaps the motivating example) seems to be:

    dt64 = numpy.datetime64(&#39;2002-06-28T01:00:00.000000000+0100&#39;)

which should be `datetime.datetime(2002, 6, 28, 1, 0)`, and not a long (!) (`1025222400000000000L`)...

Converting between datetime, Timestamp and datetime64

I am having some seemingly trivial trouble with numpy when the array contains string data.  I have the following code:    

    my_array = numpy.empty([1, 2], dtype = str)
    my_array[0, 0] = &quot;Cat&quot;
    my_array[0, 1] = &quot;Apple&quot;

Now, when I print it with `print my_array[0, :]`, the response I get is `[&#39;C&#39;, &#39;A&#39;]`, which is clearly not the expected output of Cat and Apple.  Why is that, and how can I get the right output?

Thanks!

Weird behaviour initializing a numpy array of string data

Is there a SciPy function or NumPy function or module for Python that calculates the running mean of a 1D array given a specific window?

Moving average or running mean

Can I use `~A` to invert a numpy array of booleans, instead of the rather awkward functions `np.logical_and()` and `np.invert()`? 

Indeed, `~` seems to work fine, but I can&#39;t find it in any nympy reference manual, and - more alarmingly - it certainly does _not_ work with scalars (e.g. `bool(~True)` returns `True` !), so I&#39;m a little bit worried ...

Inverting a numpy boolean array using ~

May someone please explain what a Tuple is and how to use it in a Real World Scenario. I would like to find out how this can enrich my coding experience?

What and When to use Tuple?

I need a queue of (`string`, `int`) pairs. That&#39;s easy enough:

    type job struct {
        url string
        depth int
    }

    queue := make(chan job)
    queue &lt;- job{url, depth}

are there built-in pair/tuple data types in Go? There is support for [returning multiple values][2] from a function, but AFAICT, the multiple value tuples produced are not first-class citizens in Go&#39;s type system. Is that the case?

As for the &quot;what have you tried&quot; part, the obvious syntax (from a Python programmer&#39;s POV)

    queue := make(chan (string, int))

didn&#39;t work.


  [1]: http://tour.golang.org/#71
  [2]: http://golang.org/doc/effective_go.html#multiple-returns

Pair/tuple data type in Go

I&#39;m learning Python 3 using The Quick Python Book, where the author talks about frozensets, stating that since sets are mutable and hence unhashable, thereby becoming unfit for being dictionary keys, their frozen counterparts were introduced. Other than the obvious difference that a tuple is an ordered data structure while frozenset, or more generally a set, is unordered, are there any other differences between a tuple and a frozenset?

Difference between tuples and frozensets in Python

How can I convert a list with (say) 3 elements into a tuple of size 3?

For example, let&#39;s say I have `val x = List(1, 2, 3)` and I want to convert this into `(1, 2, 3)`. How can I do this?

Convert a Scala list to a tuple?

How to convert the following  tuple:

from:

    ((&#39;aa&#39;, &#39;bb&#39;, &#39;cc&#39;), &#39;dd&#39;)

to:


    (&#39;aa&#39;, &#39;bb&#39;, &#39;cc&#39;, &#39;dd&#39;)



Content Type	Original Author	Original Content on Stackoverflow
Question	user17151	View Question on Stackoverflow
Solution 1 - Python	Mike Corcoran	View Answer on Stackoverflow

What is the inverse function of zip in python?

Python Problem Overview

Python Solutions

Solution 1 - Python

throw Error('msg') vs throw new Error('msg')

How do I put an 'if clause' in an SQL string?

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