## How to use concurrent.futures map with a tqdm progress bar

### Problem:

You have a concurrent.futures executor, e.g.

import concurrent.futures

executor = concurrent.futures.ThreadPoolExecutor(64)

Using this executor, you want to map a function over an iterable in parallel (e.g. parallel download of HTTP pages).

In order to aid interactive execution, you want to use tqdm to provide a progress bar, showing the fraction of futures

### Solution:

You can use this function:

from tqdm import tqdm
import concurrent.futures

def tqdm_parallel_map(executor, fn, *iterables, **kwargs):
"""
Equivalent to executor.map(fn, *iterables),
but displays a tqdm-based progress bar.

Does not support timeout or chunksize as executor.submit is used internally

**kwargs is passed to tqdm.
"""
futures_list = []
for iterable in iterables:
futures_list += [executor.submit(fn, i) for i in iterable]
for f in tqdm(concurrent.futures.as_completed(futures_list), total=len(futures_list), **kwargs):
yield f.result()


Note that internally, executor.submit() is used, not executor.map() because there is no way of calling concurrent.futures.as_completed() on the iterator returned by executor.map().

### Problem:

You want to download a URL to a file using the requests python library, but you want to skip the download if it doesn’t exist

### Solution:

Use the following functions:

import requests
import os.path

"""
"""
with open(filename, 'wb') as fout:
response = requests.get(url, stream=True)
response.raise_for_status()
# Write response data to file
for block in response.iter_content(4096):
fout.write(block)

"""

Returns
-------
"""
if not os.path.exists(filename):
return True
return False


## Computing bounding box for a list of coordinates in Python

### Problem:

You have a list of X/Y coordinates, for example:

coords = [(6.74219, -53.57835),
(6.74952, -53.57241),
(6.75652, -53.56289),
(6.74756, -53.56598),
(6.73462, -53.57518)]

For these coordinates you want to compute the minimum bounding box.

## Removing spans/divs with style attributes from HTML

Occasionally I have to clean up some HTML code – mostly because parts of it were pasted into a CMS like WordPress from rich text editor like Word.

I’ve noticed that the formatting I want to remove is mostly based on span and div elements with a style attribute. Therefore, I’ve written a simple Python script based on BeautifulSoup4 which will replace certain tags with their contents if they have a style attribute. While in some cases some other formatting might be destroyed by such a script, it is very useful for some recurring usecases.

## Computing the LP2980 adjust resistor using Python

The LP2980ADJ is a 50 mA LDO that be configured for an output voltage from 1.23V to 15V using a pair of resistors.

The datasheet lists a formula for the output voltage, however no easy-to-use customizable software is provided that can be used to directly compute the correct resistor in a reproducible way. Mehr lesen

The following html code can be used to create an html form that allows uploading multiple files at once:

<form enctype="multipart/form-data" method="POST" action="upload.py">
<table style="width: 100%">
<tr>
<td style="text-align: right"><input type="file" multiple="" id="files" name="files"></td>
</tr>
<tr>
<td></td>
</tr>
</table>
</form>

## Normalizing electronics engineering value notations using Python

In electronics engineering there is a wide variety of notations for values that need to be recognized by intuitive user interfaces. Examples include:

• 1fA
• 0.1A
• 0.00001
• 1e-6
• 4,5nA
• 4,500.123 A
• 4A5
• 4k0 A

The wide variety of options, including thousands separators, comma-as-decimal-separator and suffix-as-decimal-separator, optional whitespace and scientific notations makes it difficult to normalize values without using specialized libraries. Mehr lesen

## Calculating the NCP380 Ilim resistor using Python

#### Problem

You want to calculate the correct value for the Ilim resistor for the NCP380 current limiter IC with a custom current limit. Mehr lesen

## Finding the nearest E96 resistor value in Python

### Problem

You want to find the E24/E48/E96 resistor value that is closest to a given exact value programmatically using python. Mehr lesen

## Engineering for the super-lazy: Solving equations without activating your brain

### Preface

In electronics engineering, from time to time you have to use standard formulas to characterize your circuits. To what extent you need to calculate all parameters most often depends on the requirement.

For example, consider the formula for the -3dB cutoff frequency of a 1st order RC lowpass filter:

$$f_c=\frac{1}{2\pi RC}$$

Although this equation is fairly simple and most people won’t have any problem solving it for any particular variable in a few seconds, it can serve as a basic example on how to solve an equation symbolically.

One of the easiest ways of performing this task is to use SymPy, a Python library for symbolic mathematics.