How about this

    x = 3.14159265
    print(f&#39;pi = {x:.2f}&#39;)


[Docs for f-strings](https://docs.python.org/3/reference/lexical_analysis.html#f-strings)

I&#39;m working on MacOS and just starting with `react-native`.

One of the first steps to get started is to run: `react-native run-android` or `react-native run-ios`. But I&#39;m getting this error:

&lt;!-- language: lang-bash --&gt;

    react-native run-android

Result:

    Scanning folders for symlinks in /Users/ric/myprojs/albums/node_modules (6ms)
    Starting JS server...
    Building and installing the app on the device (cd android &amp;&amp; ./gradlew installDebug)...
    
    FAILURE: Build failed with an exception.
    
    * What went wrong:
    Could not determine java version from &#39;9.0.1&#39;.
    
    * Try:
    Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.
    Could not install the app on the device, read the error above for details.
    Make sure you have an Android emulator running or a device connected and have
    set up your Android development environment:
    https://facebook.github.io/react-native/docs/android-setup.html


This is what I get when I run `java --version`:

&lt;!-- language: lang-bash --&gt;

    java --version

Result:

    java 9.0.1
    Java(TM) SE Runtime Environment (build 9.0.1+11)
    Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)
    mbp:albums ric$ java --version
    java 9.0.1
    Java(TM) SE Runtime Environment (build 9.0.1+11)
    Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)

## Edit

My javac version:

&lt;!-- language: lang-bash --&gt;

    javac --version

Result:

    javac 9.0.1


Any idea on how to fix this?


React Native error: &quot;Could not determine java version from &#39;9.0.1&#39;.&quot;

&lt;!-- language-all: js --&gt;

I&#39;m trying to get startdate from the URL. 
The URL looks like `http://sitename/booking?startdate=28-08-2017`

My code is below:

aap.module.ts

        import {...};

        @NgModule({
          declarations: [
            AppComponent, ModalComponent
          ],
          imports: [
            BrowserModule,
            FormsModule,
            HttpModule,
            JsonpModule,
            ReactiveFormsModule,
            RouterModule.forRoot([{
                    path: &#39;&#39;,
                    component: AppComponent
                },
            ]),    
          ], 
          providers: [ContactService, AddonService, MainService],
          bootstrap: [AppComponent]
        })
        export class AppModule { }


aap.component.ts

    import {...}
    import {Router, ActivatedRoute, Params} from &#39;@angular/router&#39;;

    constructor(private activatedRoute: ActivatedRoute) {
      // subscribe to router event
      this.activatedRoute.queryParams.subscribe((params: Params) =&gt; {
        console.log(params);
      });

    }

But its giving the below error 

&gt; Unhandeled Promise rejection: No base href set. Please provide a value
&gt; for the APP_BASE_HREF token or add a base element to the document. ;
&gt; Zone: &lt;root&gt; ; Task: Promise.then ; Value: Error: No base href set.
&gt; Please provide a value for the APP_BASE_HREF token or add a base
&gt; element to the document.


How does Angular know the base href?




How to get param from url in angular 4?

Using %-formatting, I can specify the number of decimal cases in a string:

    x = 3.14159265
    print(&#39;pi = %0.2f&#39; %x)

This would give me:

    pi = 3.14

Is there any way of doing this using f-strings in Python 3.6?

Rounding floats with f-string

Using %-formatting, I can specify the number of decimal cases in a string:
<pre><code class="hljs language-ini">x = 3.14159265
print('pi = %0.2f' %x)
</code></pre>
This would give me:
<pre><code class="hljs language-ini">pi = 3.14
</code></pre>
Is there any way of doing this using f-strings in Python 3.6?

I have a url that I need to send a request to using date variables. The https address takes the date variables. I&#39;d like to assign the dates to the address string using something like the formatting operator % in Python. Does R have a similar operator or do I need to rely on paste()?

    # Example variables
    year = &quot;2008&quot;
    mnth = &quot;1&quot;
    day = &quot;31&quot;

This is what I would do in Python 2.7:

    url = &quot;https:.../KBOS/%s/%s/%s/DailyHistory.html&quot; % (year, mnth, day)

Or using .format() in 3.+.

The only I&#39;d know to do in R seems verbose and relies on paste:

    url_start = &quot;https:.../KBOS/&quot;
    url_end = &quot;/DailyHistory.html&quot;
    paste(url_start, year, &quot;/&quot;, mnth, &quot;/&quot;, day, url_end) 

Is there a better way of doing this?

Is there a string formatting operator in R similar to Python&#39;s %?

I&#39;m learning pytest and I lint my code with pylint.
But pylint still complaints about:  
`W0621: Redefining name %r from outer scope (line %s)`

for the following example from pytest:

    # test_wallet.py
    
    @pytest.fixture
    def my_wallet():
        &#39;&#39;&#39;Returns a Wallet instance with a zero balance&#39;&#39;&#39;
        return Wallet()
    
    @pytest.mark.parametrize(&quot;earned,spent,expected&quot;, [
        (30, 10, 20),
        (20, 2, 18),
    ])
    def test_transactions(my_wallet, earned, spent, expected):
        my_wallet.add_cash(earned)
        my_wallet.spend_cash(spent)
        assert my_wallet.balance == expected

Redefining name `my_wallet` from outer scope.

I found workaround to add `_` prefix to the fixture name: `_my_wallet`.

What would be the best practice if I want to keep fixtures in same file as functions?  

 1. Prepend all fixtures with `_`?
 2. Disable this `pylint` check for tests?
 3. Better suggestion?

pytest fixtures Redefining name from outer scope [pylint]

I want to allow type hinting using Python 3 to accept sub classes of a certain class. E.g.:

    class A:
        pass

    class B(A):
        pass

    class C(A):
        pass
    
    def process_any_subclass_type_of_A(cls: A):
        if cls == B:
            # do something
        elif cls == C:
            # do something else

Now when typing the following code:

    process_any_subclass_type_of_A(B)

I get an PyCharm IDE hint &#39;Expected type A, got Type[B] instead.&#39;

How can I change type hinting here to accept any subtypes of A?

According to [PEP 484][1] (&quot;Expressions whose type is a subtype of a specific argument type are also accepted for that argument.&quot;), I understand that my solution `(cls: A)` should work?


  [1]: https://www.python.org/dev/peps/pep-0484/#type-definition-syntax

Subclass in type hinting

I have a large dataframe containing lots of columns.

For each row/index in the dataframe I do some operations, read in some ancilliary ata, etc and get a new value. Is there a way to add that new value into a new column at the correct row/index?

I can use .assign to add a new column but as I&#39;m looping over the rows and only generating the data to add for one value at a time (generating it is quite involved). When it&#39;s generated I&#39;d like to immediately add it to the dataframe rather than waiting until I&#39;ve generated the entire series.

This doesn&#39;t work and gives a key error:

    df[&#39;new_column_name&#39;].iloc[this_row]=value

Do I need to initialise the column first or something?

Pandas - add value at specific iloc into new dataframe column

I want to import sklearn but there is no module apparently:

    ModuleNotFoundError: No module named &#39;sklearn&#39;

I am using Anaconda and `Python 3.6.1`; I have checked everywhere but still can&#39;t find answers.

When I use the command:
`conda install scikit-learn` should this not just work? 
&lt;br&gt;**Where does anaconda install the package?**

I was checking the frameworks in my python library and there was nothing about sklearn only numpy and scipy.

Please help, I am new to using python packages especially via anaconda.


ModuleNotFoundError: No module named &#39;sklearn&#39;

I am learning to use &#39;pillow 5.0&#39; following book &#39;Automate the boring stuff with python&#39;

The info about the image object

    In [79]: audacious = auda
    In [80]: print(audacious.format, audacious.size, audacious.mode)
    PNG (1094, 960) RGBA

When I tried to convert filetype, it report error.

    In [83]: audacious.save(&#39;audacious.jpg&#39;)
    OSError: cannot write mode RGBA as JPEG
There&#39;s no such a
n error in book.

cannot write mode RGBA as JPEG

I am moving my config from setup.py to setup.cfg and having issues setting up the `entry_points` parameter. At the moment I am using a hybrid approach which works, however, I would like to move the `entry_points` to setup.cfg.

From 

    def setup_package():
        setup(version=get_version(),
              entry_points={&#39;console_scripts&#39;:[&#39;app=my_package.app.run:cli&#39;],})

to

```cfg
[metadata]
name = my-package
description = my-package
license = unlicensed
long-description = README.md
platforms = any
classifiers =
  Programming Language :: Python

[options]
zip_safe = False
packages = my_package,  my_package.app
include_package_data = True
package_dir =
  = .
tests_require = pytest; pytest-cov

[entry_points]
console_scripts =
  my-package = my_package.app.run:cli
```

How to set up entry_points in setup.cfg

Suppose you want to constrain a type variable to implement a certain interface. You might write something like so:

    from typing import TypeVar, Callable

    T = TypeVar(&#39;T&#39;, Callable)

    class Foo(Generic[T]):
        ...

    &gt;&gt; TypeError: A single constraint is not allowed

Why is Python unhappy about this use of type constraints? [PEP 484](https://www.python.org/dev/peps/pep-0484/#generics) and the [Python source code](https://github.com/python/typing/blob/master/src/typing.py#L511) are unhelpful in this regard.

Note: in my particular case I am interested in constraining a type variable to implement an abstract base class, but the principle is the same.

Why are single type constraints disallowed in Python?

I&#39;m trying to install tensorflow onto a Mac with Python3.7. However, I&#39;m getting the error:

    $ pip3 -v install tensorflow
    ...    
        Skipping link https://files.pythonhosted.org/packages/56/7a/c6bca0fe52a94ca508731d8b139e7dbd5a36cddc64c19f422f97e5a853e8/tensorflow-1.10.0rc1-cp36-cp36m-win_amd64.whl#sha256=3ab24374888d6a13d55ce2e3cf4ba0c9cd6f824723313db5322512087525cb78 (from https://pypi.org/simple/tensorflow/); it is not compatible with this Python
      Could not find a version that satisfies the requirement tensorflow (from versions: )
    Cleaning up...
    Removed build tracker &#39;/private/var/folders/4n/9342s4wd3jv0qzwjz8rxrygr0000gp/T/pip-req-tracker-3p60r2lo&#39;

    No matching distribution found for tensorflow

From what I can gather this is happening because tensorflow doesn&#39;t yet support Python3.7. As a workaround I want to install Python3.6 alongside 3.7 and then install tensorflow to that version. However, I&#39;m new to Mac and not sure of the correct way to do this without potentially messing with the preexisting Python version. 

I&#39;ve tried using brew, but it looks like Python3 is as specific as it gets. What is the correct way to do what I&#39;m after?

Installing Python3.6 alongside Python3.7 on Mac

I tried to read https://hackernoon.com/asynchronous-python-45df84b82434.
It&#39;s about asynchronous python and I tried the code from this, but I&#39;m getting a weird Error.
The code is:
`

    import asyncio
    import aiohttp
    
    urls = [&#39;http://www.google.com&#39;, &#39;http://www.yandex.ru&#39;, &#39;http://www.python.org&#39;]
    
    async def call_url(url):
        print(&#39;Starting {}&#39;.format(url))
        response = await aiohttp.ClientSession().get(url)
        data = await response.text()
        print(&#39;{}: {} bytes: {}&#39;.format(url, len(data), data))
        return data
    
    futures = [call_url(url) for url in urls]
    
    asyncio.run(asyncio.wait(futures))


When I try to run it says:

    
    Traceback (most recent call last):
      File &quot;test.py&quot;, line 15, in &lt;module&gt;
        asyncio.run(asyncio.wait(futures))
    AttributeError: module &#39;asyncio&#39; has no attribute &#39;run&#39;
    sys:1: RuntimeWarning: coroutine &#39;call_url&#39; was never awaited
    
    

I dont have any files named ayncio and I have proof:

    &gt;&gt;&gt; asyncio
    &lt;module &#39;asyncio&#39; from &#39;/usr/lib/python3.6/asyncio/__init__.py&#39;&gt;


Content Type	Original Author	Original Content on Stackoverflow
Question	elsoja	View Question on Stackoverflow
Solution 1 - Python	JBernardo	View Answer on Stackoverflow

Rounding floats with f-string

Python Problem Overview

Python Solutions

Solution 1 - Python

How to get param from url in angular 4?

React Native error: "Could not determine java version from '9.0.1'."

Attributions