you need to iterate over `dict.iteritems()`:

    for k,v in d.iteritems():               # will become d.items() in py3k
      print &quot;%s - %s&quot; % (str(k), str(v))

Update: in py3 V3.6+

    for k,v in d.items():
      print (f&quot;{k} - {v}&quot;)

if you are using Python 3.6

    from collections import defaultdict
    
    for k, v in d.items():
        print(f&#39;{k} - {v}&#39;)

If you want to iterate over individual item on an individual collection:

    from collections import defaultdict

    for k, values in d.items():
        for value in values:
           print(f&#39;{k} - {value}&#39;)

I&#39;m trying to compare two numbers in R as a part of a if-statement condition:

`(a-b) &gt;= 0.5`

In this particular instance, a = 0.58 and b = 0.08... and yet `(a-b) &gt;= 0.5` is false.  I&#39;m aware of the dangers of using `==` for exact number comparisons, and this seems related:

`(a - b) == 0.5)` is false, while 

`all.equal((a - b), 0.5)` is true.

The only solution I can think of is to have two conditions: `(a-b) &gt; 0.5 | all.equal((a-b), 0.5)`.  This works, but is that really the only solution?  Should I just swear off of the `=` family of comparison operators forever?


**Edit for clarity:** I know that this is a floating point problem.  More fundamentally, what I&#39;m asking is: what should I do about it?  What&#39;s a sensible way to deal with greater-than-or-equal-to comparisons in R, since the `&gt;=` can&#39;t really be trusted?

Numeric comparison difficulty in R

I&#39;m trying to write a SQL Server database update script. I want to test for the existence of a column in a table, then if it doesn&#39;t exist add the column with a default value, and finally update that column based on the current value of a different column in the same table. I want this script to be runnable multiple times, the first time updating the table and on subsequent runs the script should be ignored. My script currently looks like the following:

    IF NOT EXISTS(SELECT * FROM INFORMATION_SCHEMA.COLUMNS
    	WHERE TABLE_NAME = &#39;PurchaseOrder&#39; AND COLUMN_NAME = &#39;IsDownloadable&#39;)
    BEGIN
    
    ALTER TABLE [dbo].[PurchaseOrder] ADD [IsDownloadable] bit NOT NULL DEFAULT 0
    
    UPDATE [dbo].[PurchaseOrder] SET [IsDownloadable] = 1 WHERE [Ref] IS NOT NULL
    
    END

SQL Server returns error &quot;Invalid column name &#39;IsDownloadable&#39;&quot;, i.e. I need to commit the DDL before I can update the column. I&#39;ve tried various permutations but I&#39;m getting nowhere fast.

Test Column exists, Add Column, and Update Column

The following works as expected:

    d = [(1,2), (3,4)]
    for k,v in d:
      print &quot;%s - %s&quot; % (str(k), str(v))

But this fails:

    d = collections.defaultdict(int)
    d[1] = 2
    d[3] = 4
    for k,v in d:
      print &quot;%s - %s&quot; % (str(k), str(v))

With:

    Traceback (most recent call last):  
     File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt;  
    TypeError: &#39;int&#39; object is not iterable 

Why? How can i fix it?

Iterating over key and value of defaultdict dictionaries

The following works as expected:
<pre><code class="hljs language-css">d = [(1,2), (3,4)]
for k,v in d:
 print "%s - %s" % (str(k), str(v))
</code></pre>
But this fails:
<pre><code class="hljs language-css">d = collections.defaultdict(int)
d[1] = 2
d[3] = 4
for k,v in d:
 print "%s - %s" % (str(k), str(v))
</code></pre>
With:
<pre><code class="hljs language-vbnet">Traceback (most recent call last): 
 File "&#x3C;stdin>", line 1, in &#x3C;module> 
TypeError: 'int' object is not iterable 
</code></pre>
Why? How can i fix it?

I have text file which I want to erase in Python. How do I do that?

How to erase the file contents of text file in Python?

Is it possible to have multiple models included in a single `ModelForm` in django?  I am trying to create a profile edit form.  So I need to include some fields from the User model **and** the UserProfile model.  Currently I am using 2 forms like this

    class UserEditForm(ModelForm):
    
        class Meta:
            model = User
            fields = (&quot;first_name&quot;, &quot;last_name&quot;)
    
    class UserProfileForm(ModelForm):
    
        class Meta:
            model = UserProfile
            fields = (&quot;middle_name&quot;, &quot;home_phone&quot;, &quot;work_phone&quot;, &quot;cell_phone&quot;)


Is there a way to consolidate these into one form or do I just need to create a form and handle the db loading and saving myself?


Multiple Models in a single django ModelForm?

I have the below db model:

    from datetime import datetime    

    class TermPayment(models.Model):
        # I have excluded fields that are irrelevant to the question
        date = models.DateTimeField(default=datetime.now(), blank=True)
    
I add a new instance by using the below:

    tp = TermPayment.objects.create(**kwargs)

My issue: all records in database have the same value in date field, which is the date of the first payment. After the server restarts, one record has the new date and the other records have the same as the first. It looks as if some data is cached, but I can&#39;t find where.

database: mysql 5.1.25

django v1.1.1



Django datetime issues (default=datetime.now())

I&#39;ve a problem with JSON in python.

In fact, if I try to execute this code, python gives me a sorted JSON string! 

For example:

```
values = {
  &#39;profile&#39;: &#39;testprofile&#39;,
  &#39;format&#39;: &#39;RSA_RC4_Sealed&#39;,
  &#39;enc_key&#39;: base64.b64encode(chiave_da_inviare),
  &#39;request&#39;: base64.b64encode(data)
}

values_json = json.dumps(values, sort_keys = False, separators = (&#39;,&#39;, &#39;:&#39;))
```

And this is the output:

```
{
  &quot;profile&quot;: &quot;testprofile&quot;,
  &quot;enc_key&quot;: &quot;GBWo[...]NV6w==&quot;,
  &quot;request&quot;: &quot;TFl[...]uYw==&quot;,
  &quot;format&quot;: &quot;RSA_RC4_Sealed&quot;
}
```

As you can see, I tried to use &quot;sort_keys=False&quot; but nothing changed.

How can I stop Python sorting my JSON strings?

JSON output sorting in Python

I have to create an &quot;Expires&quot; value 5 minutes in the future, but I have to supply it in UNIX Timestamp format.  I have this so far, but it seems like a hack.

    def expires():
        &#39;&#39;&#39;return a UNIX style timestamp representing 5 minutes from now&#39;&#39;&#39;
        epoch = datetime.datetime(1970, 1, 1)
        seconds_in_a_day = 60 * 60 * 24
        five_minutes = datetime.timedelta(seconds=5*60)
        five_minutes_from_now = datetime.datetime.now() + five_minutes
        since_epoch = five_minutes_from_now - epoch
        return since_epoch.days * seconds_in_a_day + since_epoch.seconds

Is there a module or function that does the timestamp conversion for me?



Python Create unix timestamp five minutes in the future

How may Wiktionary&#39;s API be used to determine whether or not a word exists?



How can I retrieve Wiktionary word content?

I&#39;m requesting data from a server which returns data in the JSON format. Casting a HashMap into JSON when making the request wasn&#39;t hard at all but the other way seems to be a little tricky. The JSON response looks like this:

```json
{ 
	&quot;header&quot; : { 
		&quot;alerts&quot; : [ 
			{
				&quot;AlertID&quot; : &quot;2&quot;,
				&quot;TSExpires&quot; : null,
				&quot;Target&quot; : &quot;1&quot;,
				&quot;Text&quot; : &quot;woot&quot;,
				&quot;Type&quot; : &quot;1&quot;
			},
			{ 
				&quot;AlertID&quot; : &quot;3&quot;,
				&quot;TSExpires&quot; : null,
				&quot;Target&quot; : &quot;1&quot;,
				&quot;Text&quot; : &quot;woot&quot;,
				&quot;Type&quot; : &quot;1&quot;
			}
		],
		&quot;session&quot; : &quot;0bc8d0835f93ac3ebbf11560b2c5be9a&quot;
	},
	&quot;result&quot; : &quot;4be26bc400d3c&quot;
}
```

What way would be easiest to access this data? I&#39;m using the GSON module.

How can I convert JSON to a HashMap using Gson?

    d3 = dict(d1, **d2)


I understand that this merges the dictionary. But, is it unique? What if d1 has the same key as d2 but different value?  I would like d1 and d2 to be merged, but d1 has priority if there is duplicate key.

How do I merge dictionaries together in Python?

I&#39;m trying to get the key of the maximum value in the `Dictionary&lt;string, double&gt; results`.

This is what I have so far:

    double max = results.Max(kvp =&gt; kvp.Value);
    return results.Where(kvp =&gt; kvp.Value == max).Select(kvp =&gt; kvp.Key).First();

However, since this seems a little inefficient, I was wondering whether there was a better way to do this.

Good way to get the key of the highest value of a Dictionary in C#

Having some maps defined as:

    var valueToSomeType = map[uint8]someType{...}
    var nameToSomeType = map[string]someType{...}

I would want a variable that points to the address of the maps (to don&#39;t copy all variable). I tried it using:

    valueTo := &amp;valueToSomeType
    nameTo := &amp;nameToSomeType

but at using `valueTo[number]`, it shows  
*internal compiler error: var without type, init: new*

How to get it?

**Edit**  

The error was showed by another problem.

Pointer to a map

What is the difference between iterators and generators? Some examples for when you would use each case would be helpful.

Difference between Python&#39;s Generators and Iterators

I need to go through a set and remove elements that meet a predefined criteria.

This is the test code I wrote:

    #include &lt;set&gt;
    #include &lt;algorithm&gt;

    void printElement(int value) {
        std::cout &lt;&lt; value &lt;&lt; &quot; &quot;;
    }

    int main() {
        int initNum[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
        std::set&lt;int&gt; numbers(initNum, initNum + 10);
        // print &#39;0 1 2 3 4 5 6 7 8 9&#39;
        std::for_each(numbers.begin(), numbers.end(), printElement);

        std::set&lt;int&gt;::iterator it = numbers.begin();

        // iterate through the set and erase all even numbers
        for (; it != numbers.end(); ++it) {
            int n = *it;
            if (n % 2 == 0) {
                // wouldn&#39;t invalidate the iterator?
                numbers.erase(it);
            }
        }

        // print &#39;1 3 5 7 9&#39;
        std::for_each(numbers.begin(), numbers.end(), printElement);

        return 0;
    }

At first, I thought that erasing an element from the set while iterating through it would invalidate the iterator, and the increment at the for loop would have undefined behavior. Even though, I executed this test code and all went well, and I can&#39;t explain why.

**My question:**
Is this the defined behavior for std sets or is this implementation specific? I am using gcc 4.3.3 on ubuntu 10.04 (32-bit version), by the way.

Thanks!

**Proposed solution:**

Is this a correct way to iterate and erase elements from the set?

    while(it != numbers.end()) {
        int n = *it;
        if (n % 2 == 0) {
            // post-increment operator returns a copy, then increment
            numbers.erase(it++);
        } else {
            // pre-increment operator increments, then return
            ++it;
        }
    }

**Edit: PREFERED SOLUTION**

I came around a solution that seems more elegant to me, even though it does exactly the same.

    while(it != numbers.end()) {
        // copy the current iterator then increment it
        std::set&lt;int&gt;::iterator current = it++;
        int n = *current;
        if (n % 2 == 0) {
            // don&#39;t invalidate iterator it, because it is already
            // pointing to the next element
            numbers.erase(current);
        }
    }

If there are several test conditions inside the while, each one of them must increment the iterator. I like this code better because the iterator is incremented **only in one place**, making the code less error-prone and more readable.

Deleting elements from std::set while iterating

I have a multi-line string defined like this:

    foo = &quot;&quot;&quot;
    this is 
    a multi-line string.
    &quot;&quot;&quot;

This string we used as test-input for a parser I am writing. The parser-function receives a `file`-object as input and iterates over it. It does also call the `next()` method directly to skip lines, so I really need an iterator as input, not an iterable.
I need an iterator that iterates over the individual lines of that string like a `file`-object would over the lines of a text-file. I could of course do it like this:

    lineiterator = iter(foo.splitlines())

Is there a more direct way of doing this? In this scenario the string has to traversed once for the splitting, and then again by the parser. It doesn&#39;t matter in my test-case, since the string is very short there, I am just asking out of curiosity. Python has so many useful and efficient built-ins for such stuff, but I could find nothing that suits this need.

Iterate over the lines of a string

Currently I&#39;m doing this:

    try:
        something = iterator.next()
        # ...
    except StopIteration:
        # ...

But I would like an expression that I can place inside a simple `if` statement.
Is there anything built-in which would make this code look less clumsy?

`any()` returns `False` if an iterable is empty, but it will potentially iterate over all the items if it&#39;s not.
I only need it to check the first item.

---

Someone asks what I&#39;m trying to do.
I have written a function which executes an SQL query and yields its results.
Sometimes when I call this function I just want to know if the query returned anything and make a decision based on that.

One-liner to check whether an iterator yields at least one element?

Can I reset an iterator / generator in Python?  I am using DictReader and would like to reset it to the beginning of the file.

Content Type	Original Author	Original Content on Stackoverflow
Question	Georg Fritzsche	View Question on Stackoverflow
Solution 1 - Python	SilentGhost	View Answer on Stackoverflow
Solution 2 - Python	Vlad Bezden	View Answer on Stackoverflow
Solution 3 - Python	Nguai al	View Answer on Stackoverflow

Iterating over key and value of defaultdict dictionaries

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Solution 3 - Python

Test Column exists, Add Column, and Update Column

Numeric comparison difficulty in R

Attributions