Threading in a PyQt application: Use Qt threads or Python threads?

| | | |

👻 Check our latest review to choose the best laptop for Machine Learning engineers and Deep learning tasks!

I"m writing a GUI application that regularly retrieves data through a web connection. Since this retrieval takes a while, this causes the UI to be unresponsive during the retrieval process (it cannot be split into smaller parts). This is why I"d like to outsource the web connection to a separate worker thread.

[Yes, I know, now I have two problems.]

Anyway, the application uses PyQt4, so I"d like to know what the better choice is: Use Qt"s threads or use the Python threading module? What are advantages / disadvantages of each? Or do you have a totally different suggestion?

Edit (re bounty): While the solution in my particular case will probably be using a non-blocking network request like Jeff Ober and Lukáš Lalinský suggested (so basically leaving the concurrency problems to the networking implementation), I"d still like a more in-depth answer to the general question:

What are advantages and disadvantages of using PyQt4"s (i.e. Qt"s) threads over native Python threads (from the threading module)?


Edit 2: Thanks all for you answers. Although there"s no 100% agreement, there seems to be widespread consensus that the answer is "use Qt", since the advantage of that is integration with the rest of the library, while causing no real disadvantages.

For anyone looking to choose between the two threading implementations, I highly recommend they read all the answers provided here, including the PyQt mailing list thread that abbot links to.

There were several answers I considered for the bounty; in the end I chose abbot"s for the very relevant external reference; it was, however, a close call.

Thanks again.

👻 Read also: what is the best laptop for engineering students?

Threading in a PyQt application: Use Qt threads or Python threads? log: Questions

log

Python"s equivalent of && (logical-and) in an if-statement

5 answers

delete By delete

Here"s my code:

def front_back(a, b):
  # +++your code here+++
  if len(a) % 2 == 0 && len(b) % 2 == 0:
    return a[:(len(a)/2)] + b[:(len(b)/2)] + a[(len(a)/2):] + b[(len(b)/2):] 
  else:
    #todo! Not yet done. :P
  return

I"m getting an error in the IF conditional.
What am I doing wrong?

934

Answer #1

You would want and instead of &&.

934

Answer #2

Python uses and and or conditionals.

i.e.

if foo == "abc" and bar == "bac" or zoo == "123":
  # do something

Threading in a PyQt application: Use Qt threads or Python threads? log: Questions

log

How do you get the logical xor of two variables in Python?

5 answers

Zach Hirsch By Zach Hirsch

How do you get the logical xor of two variables in Python?

For example, I have two variables that I expect to be strings. I want to test that only one of them contains a True value (is not None or the empty string):

str1 = raw_input("Enter string one:")
str2 = raw_input("Enter string two:")
if logical_xor(str1, str2):
    print "ok"
else:
    print "bad"

The ^ operator seems to be bitwise, and not defined on all objects:

>>> 1 ^ 1
0
>>> 2 ^ 1
3
>>> "abc" ^ ""
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for ^: "str" and "str"
794

Answer #1

If you"re already normalizing the inputs to booleans, then != is xor.

bool(a) != bool(b)

sep

How to print number with commas as thousands separators?

5 answers

I am trying to print an integer in Python 2.6.1 with commas as thousands separators. For example, I want to show the number 1234567 as 1,234,567. How would I go about doing this? I have seen many examples on Google, but I am looking for the simplest practical way.

It does not need to be locale-specific to decide between periods and commas. I would prefer something as simple as reasonably possible.

929

Answer #1

Locale unaware

"{:,}".format(value)  # For Python ‚â•2.7
f"{value:,}"  # For Python ‚â•3.6

Locale aware

import locale
locale.setlocale(locale.LC_ALL, "")  # Use "" for auto, or force e.g. to "en_US.UTF-8"

"{:n}".format(value)  # For Python ‚â•2.7
f"{value:n}"  # For Python ‚â•3.6

Reference

Per Format Specification Mini-Language,

The "," option signals the use of a comma for a thousands separator. For a locale aware separator, use the "n" integer presentation type instead.

929

Answer #2

I got this to work:

>>> import locale
>>> locale.setlocale(locale.LC_ALL, "en_US")
"en_US"
>>> locale.format("%d", 1255000, grouping=True)
"1,255,000"

Sure, you don"t need internationalization support, but it"s clear, concise, and uses a built-in library.

P.S. That "%d" is the usual %-style formatter. You can have only one formatter, but it can be whatever you need in terms of field width and precision settings.

P.P.S. If you can"t get locale to work, I"d suggest a modified version of Mark"s answer:

def intWithCommas(x):
    if type(x) not in [type(0), type(0L)]:
        raise TypeError("Parameter must be an integer.")
    if x < 0:
        return "-" + intWithCommas(-x)
    result = ""
    while x >= 1000:
        x, r = divmod(x, 1000)
        result = ",%03d%s" % (r, result)
    return "%d%s" % (x, result)

Recursion is useful for the negative case, but one recursion per comma seems a bit excessive to me.

sep

How would you make a comma-separated string from a list of strings?

5 answers

mweerden By mweerden

What would be your preferred way to concatenate strings from a sequence such that between every two consecutive pairs a comma is added. That is, how do you map, for instance, ["a", "b", "c"] to "a,b,c"? (The cases ["s"] and [] should be mapped to "s" and "", respectively.)

I usually end up using something like "".join(map(lambda x: x+",",l))[:-1], but also feeling somewhat unsatisfied.

612

Answer #1

my_list = ["a", "b", "c", "d"]
my_string = ",".join(my_list)
"a,b,c,d"

This won"t work if the list contains integers


And if the list contains non-string types (such as integers, floats, bools, None) then do:

my_string = ",".join(map(str, my_list)) 

We hope this article has helped you to resolve the problem. Apart from Threading in a PyQt application: Use Qt threads or Python threads?, check other log-related topics.

Want to excel in Python? See our review of the best Python online courses 2022. If you are interested in Data Science, check also how to learn programming in R.

By the way, this material is also available in other languages:



Oliver Lehnman

Abu Dhabi | 2022-12-01

Simply put and clear. Thank you for sharing. Threading in a PyQt application: Use Qt threads or Python threads? and other issues with StackOverflow was always my weak point 😁. Checked yesterday, it works!

Walter Lehnman

Warsaw | 2022-12-01

Maybe there are another answers? What Threading in a PyQt application: Use Qt threads or Python threads? exactly means?. I am just not quite sure it is the best method

Jan Ungerschaft

Shanghai | 2022-12-01

Simply put and clear. Thank you for sharing. Threading in a PyQt application: Use Qt threads or Python threads? and other issues with split was always my weak point 😁. Checked yesterday, it works!

Shop

Learn programming in R: courses

$

Best Python online courses for 2022

$

Best laptop for Fortnite

$

Best laptop for Excel

$

Best laptop for Solidworks

$

Best laptop for Roblox

$

Best computer for crypto mining

$

Best laptop for Sims 4

$

Latest questions

NUMPYNUMPY

Common xlabel/ylabel for matplotlib subplots

12 answers

NUMPYNUMPY

How to specify multiple return types using type-hints

12 answers

NUMPYNUMPY

Why do I get "Pickle - EOFError: Ran out of input" reading an empty file?

12 answers

NUMPYNUMPY

Flake8: Ignore specific warning for entire file

12 answers

NUMPYNUMPY

glob exclude pattern

12 answers

NUMPYNUMPY

How to avoid HTTP error 429 (Too Many Requests) python

12 answers

NUMPYNUMPY

Python CSV error: line contains NULL byte

12 answers

NUMPYNUMPY

csv.Error: iterator should return strings, not bytes

12 answers

News


Wiki

Python | How to copy data from one Excel sheet to another

Common xlabel/ylabel for matplotlib subplots

Check if one list is a subset of another in Python

sin

How to specify multiple return types using type-hints

exp

Printing words vertically in Python

exp

Python Extract words from a given string

Cyclic redundancy check in Python

Finding mean, median, mode in Python without libraries

cos

Python add suffix / add prefix to strings in a list

Why do I get "Pickle - EOFError: Ran out of input" reading an empty file?

Python - Move item to the end of the list

Python - Print list vertically