Jose Cuervo posted:

For better or worse I chose PySide and am having reasonable success. I can make the tabbed layout work as accipter suggested below by locking the tabs (disabling them), and maybe if I have more time on my hands than I know what to do with I will look into prettying things up.


So the for loop that iterates over the n simulation replications is in the main_gui function. Each time a simulation replication is completed, I would like the progress bar to update. I don't know how I would send a signal from the for loop in main_gui to the progress bar. Any pointers?

New questions:
In one of my tabs I have a button that, when clicked, dynamically adds a QGroupBox of widgets to the tab. By clicking multiple times on the button you can add multiple QGroupBoxes of the widgets. My problem now is determining how to access/ reference the dynamically added QGroupBoxes and the widgets inside of them. Here is the code:

Python code:

snip

Eventually I need to be able to access the type of fuel selected in each group box, the capacity of the tanker in each group box, and the number of tankers of that type. For right now I was trying to update the title of the group box using signals (specifically the currentIndexChanged signal of the QComboBox). What happens though is that if I add two group boxes, and then try to change the type of fuel in the first QComboBox, it is actually the title of the second group box that changes.

Any insight into why this is happening/ how to change it would be nice. Also any advice on how to access the type of fuel etc in each dynamically added widget.

Fergus Mac Roich posted:

It's better if the object doesn't know how to construct its dependencies. If the dependencies are available via the API at the time you construct the object, you should make the API call somewhere in the calling code and then supply the dependencies as arguments to the constructor. Or maybe I write too much java.

Jose Cuervo posted:

So the for loop that iterates over the n simulation replications is in the main_gui function. Each time a simulation replication is completed, I would like the progress bar to update. I don't know how I would send a signal from the for loop in main_gui to the progress bar. Any pointers?

QuarkJets posted:

Each time that you call add_tanker_type, you're explicitly reassigning the contents of self.tanker_type_gb. Since modify_gb_title is operating on self.tanker_type_gb, it's operating on whatever was last assigned.

One thing that you can do instead is append to an internal list of that holds QGroupBox items, then in modify_gb_title you modify the title of whatever index has been selected. You can do this because the currentIndexChanged signal won't just call the function that you connect to it, it'll also call that function with the value of the new index (if you let it).

Python code:

   def __init__(self, the_parent):
        .... # code to initialize class
        self.tanker_type_gb_list = []

    def add_tanker_type(self):
        tanker_type_gb_new = QtGui.QGroupBox("Tanker Type %s" % (len(self.tanker_type_gb_list) + 1), self)
        tanker_type_gb_new.setMaximumHeight(100)
        self.tanker_type_gb_list.append(tanker_type_gb_new)
        tanker_type_fl = QtGui.QFormLayout()
        tanker_fuel = QtGui.QComboBox()
        tanker_fuel.addItem("Diesel")
        tanker_fuel.addItem("Regular")
        tanker_fuel.addItem("Supreme")
        tanker_fuel.currentIndexChanged.connect(self.modify_gb_title)
       .... # other code in this method

    # QComboBox.currentIndexChanged comes with an integer for the new index!
    def modify_gb_title(self, ind):
        tanker_type_gb = self.tanker_type_gb_list[ind]
        current_title = tanker_type_gb.title()
        ... # etc

See http://doc.qt.io/qt-4.8/qcombobox.html#currentIndex-prop
Basically QComboBox.currentIndexChanged will call whatever function that you give it with an integer, if you let it. That integer is the new selected index in that QComboBox. By passing that integer to modify_gb_title, you can modify the correct QGroupBox by using that index to access your list of QGroupBox items.

This also solves the problem where you don't have easy access to those QGroupBox items. Instead of reassigning an attribute each time that you create a new QGroupBox, just append the new QGroupBox to a list. Then you have access to any of the created QGroupBox items.

accipter posted:

Take a look at this simple example: https://gist.github.com/arkottke/7c1c33fc6fd697cde9c88c2b47fa06ea

I would also point you to the mandelbrot example (https://github.com/PySide/Examples/blob/master/examples/threads/mandelbrot.py).

Jose Cuervo posted:

Thank you for this example, I am looking through it currently and trying to make sure I understand what everything does.

EDIT:
I think I now have a better grasp on signals and slots. updateRange is a signal that sends out two values (min and max of the range), and you connect it to self.progressBar.setRange which is a slot that takes two values, correct?

The .emit() part means that the signal gets sent, correct?

I am still running into the warning message from the joblib library. Is the answer to that in the Mandelbrot example? I haven't had a chance to look at it line by line, but on a quick read through I did not see that I could find the answer to the joblib question in there.

Jose Cuervo posted:

If I understand the code correctly, modify_gb_title is now being passed the index of the option selected in the QComboBox, correct? If so, the line tanker_type_gb = self.tanker_type_gb_list[ind] will not work because ind does NOT refer to the index of the QGroupBox whose QComboBox was changed, correct? So how do I get a reference to the QGroupBox that had a child widget edited?

quote:

Assuming I am able to figure out how to get the index of the QGroupBox that had a child widget edited, I would now like to find the QLineEdit corresponding to the row in the QFormLayout titled 'Number of tankers'. I know I can get a reference to the QFormLayout with:

Python code:

snip

but the call to widget.children() returns an empty list. However the call to tanker_type_gb.children() returns a list that does contain the QLabels and QLineEdits:

Python code:

snip

Can I always expect that tanker_type_gb.children()[1] and tanker_type_gb.children()[2] will be the QLabel and QLineEdit respectively corresponding to the first row in QFormLayout? If not, what it the idiomatic way to look through this list and find the QLineEdit corresponding to the QLabel with text "Number of tankers'?

Pumpy Dumper posted:

Ok so I have this problem that I can't seem to figure out the best way to approach:

I have two lists

list1 = A bunch of strings
list2 = another group of strings that are also all present in list1

What I want to do is take every item in list2 and check if it's in list1. If it is found then it should be removed from the corresponding item. The problem is that the list2 items are embedded within the list1 items, surrounded by other things. So what I was trying to do was figure a way to insert the list2 item into a regex search and then check that against the items in list1.

QuarkJets posted:

Oh, right, my bad.

You could create a subclass of QGroupBox (for demonstration purposes I'll call it Foo) that contains a QComboBox, and then you connect the items' signals to a Foo method, which would then cause that Foo instance to change its own title. That would do it for sure, since each QComboBox would be emitting a signal that is only connected to its own instance of the Foo class.


If you never change the order in which you're adding things to the QFormLayout, then yes, that children order will be the same every time. Don't do this though, because it's sloppy and a very fragile implementation. If you just define your own TankerType class then you can easily avoid having to do that.

Jose Cuervo posted:

Slots/Signals question:

I would like to run a function that takes arguments (for instance my_func(int, str, int)) when a QtGui.QPushButton is clicked. The following code

Python code:

my_btn = QtGui.QPushButton()
my_btn.clicked.connect(my_func(my_int, my_str, my_second_int))

produces the following RuntimeError: Failed to connect signal clicked().

How can I accomplish this?

quote:

s.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)

Jose Cuervo posted:

OK, I will rewrite the code as a class.

Slots/Signals question:

I would like to run a function that takes arguments (for instance my_func(int, str, int)) when a QtGui.QPushButton is clicked. The following code

Python code:

my_btn = QtGui.QPushButton()
my_btn.clicked.connect(my_func(my_int, my_str, my_second_int))

produces the following RuntimeError: Failed to connect signal clicked().

How can I accomplish this?

Pumpy Dumper posted:

Question: I don't really understand how zip() works. I managed to find an example to create tuples of n=2 with the following code:

code:

	
def pairwise(self, iterable):
    a, b = tee(iterable)
    next(b, None)
    return zip(a, b)

But I want to change it so that it creates tuples of three, and I can't really figure out how to do that. If I just add another variable c it prints tuples of 3 but the first two items repeat themselves.

QuarkJets posted:

The zip function takes any number of iterables and returns an iterator that returns tuples that exactly match the first, second, third, etc. values of those iterables.

code:

a = [1, 2, 3]
b = [4, 5, 6]
c = [7, 8, 9]
iter = zip(a, b, c)
for item in iter:
  print item
# The above prints (1, 4, 7), then (2, 5, 8), then (3, 6, 9)

If this is the behavior that you want, but not the behavior that you're getting, then there's likely something happening with your inputs that you didn't expect. Check your inputs to make sure that they're returning the values that you expect and in the order that you expect them

e: Sounds like you've fixed the issue

Pumpy Dumper posted:

Question: I don't really understand how zip() works. I managed to find an example to create tuples of n=2 with the following code:

code:

	
def pairwise(self, iterable):
    a, b = tee(iterable)
    next(b, None)
    return zip(a, b)

But I want to change it so that it creates tuples of three, and I can't really figure out how to do that. If I just add another variable c it prints tuples of 3 but the first two items repeat themselves.

edit: was able to get it working with the following code:

code:

	
def pairwise(self, iterable):
    a = iter(iterable)
    b = iter(iterable[1::])
    c = iter(iterable[2::])		
    return zip(a, b, c)

And it seems to work great

Gangsta Lean posted:

Your original question is, How does zip() work?
It takes any number of iterables, and iterates over all of them simultaneously. A list is an iterable, a tuple is an iterable, a dictionary is iterable, a set is iterable, a string is iterable. Even classes you create can be iterable. Here's an example using two lists.

code:

items1 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
items2 = [10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

for x in zip(items1, items2):
	print(x)

#Result is:
# (0, 10)
# (1, 11)
# (2, 12)
# (3, 13)
# (4, 14)
# (5, 15)
# (6, 16)
# (7, 17)
# (8, 18)
# (9, 19)

Your edited definition of pairwise may work for your use case, but
1. It no longer produces a pair, it is a triple - so, pairwise is a bad name for the method.
2. Your method argument is named iterable, but by using slicing, you prevent iterables that don't support slicing.
3. You created multiple (shallow) copies of the input (see further below).

An input that is iterable but doesn't support slicing, such as a dictionary (iterating over a dictionary gives you the keys), does this when using your pairwise function:

code:

items3 = {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, 'f': 5, 'g': 6, 'h': 7}

def pairwise(iterable):
    a = iter(iterable)
    b = iter(iterable[1::])
    c = iter(iterable[2::])		
    return zip(a, b, c)

for x in pairwise(items3):
	print(x)

# Traceback (most recent call last):
#   File "python", line 51, in <module>
#   File "python", line 41, in pairwise
# TypeError: unhashable type: 'slice'

When you used the [1::] syntax, you created a duplicate of your input. You can see this here, because only the first list is affected.

code:

items1 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
v = items1[1::]
items1[2] = 10000

print(items1)
print(v)

[0, 1, 10000, 3, 4, 5, 6, 7, 8, 9]
[1, 2, 3, 4, 5, 6, 7, 8, 9]

If you want to support all types of iterables, you want to use something more like this:

code:

import itertools

items1 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
items3 = {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, 'f': 5, 'g': 6, 'h': 7}

def threewise(iterable):
	a, b = itertools.tee(iterable)
	a, c = itertools.tee(iterable)
	next(b, None)
	next(c, None)
	next(c, None)
	return zip(a, b, c)


print('threewise a list')
for x in threewise(items1):
	print(x)
	
print('threewise a dictionary')
for x in threewise(items3):
	print(x)


# threewise a list
# (0, 1, 2)
# (1, 2, 3)
# (2, 3, 4)
# (3, 4, 5)
# (4, 5, 6)
# (5, 6, 7)
# (6, 7, 8)
# (7, 8, 9)
# threewise a dictionary
# ('f', 'c', 'h')
# ('c', 'h', 'a')
# ('h', 'a', 'd')
# ('a', 'd', 'b')
# ('d', 'b', 'g')
# ('b', 'g', 'e')

* itertools.tee() returns two independent iterators from a single iterable, so we can iterate more than once from the same input iterator. We need to do this twice so that we get three independent iterators: a, b, and c. Tee does not duplicate the input. By using it, it allows each of a, b, and c to iterate over the values of the input one item at a time, without producing three complete copies of the input.

* next() advances an iterator by one item. To set the desired starting points, we need to do this once to skip one item in b, and twice to skip two items in c.

* zip() was explained earlier.

Does this demonstrate it well enough?

Gangsta Lean posted:

Dominoes posted:

Python code:

-2 ** 2
Out[15]: -4

What am I missing? Julia, Google, and Wolfram alpha do it too, and I can't find confused SO posts on this!

QuarkJets posted:

I think that those languages do recognize that "-2" is its own integer rather than the result of the operation "0-2", but they also respect a specific order of operations when evaluating a line, and in doing so the negative sign attached to the 2 gets ignored until after the exponent gets evaluated. There are a few languages that make an exception for this case by giving unary minus a higher precedence, so that -2**2 results in +4 (I know that Excel is one of them but I don't use any of the others)

Tigren posted:

It seems like the statement is being evaluated as -1*2**2 which, following the order of operations I learned in whatever grade, would mean 2^2 then multiplied by -1.

Dominoes posted:

Thx. Thought I was losing it! This works: (-2) ** 2

Scratching my head as to why they'd all set it up that way.

Hubis posted:

I don't know any language that would determine " - x [op] y" as "(-x) [op] y" (in the general case).

taqueso posted:

I was trying to think of where this might not be true, and in Rust, it seems like the unary operators (including -) have higher precedence than binary operators.

code:

fn main() {
    let x = 5;
    assert_eq!(  - x + 1     ,    -4);
    assert_eq!(  - (x + 1)   ,    -6);
    assert_eq!(  (- x) + 1   ,    -4);
}

https://play.rust-lang.org/?gist=0f0c7aecaa04d12beb7c23c369680f06&version=nightly&backtrace=0

Dominoes posted:

I feel like this falls into the same category as floating-point peculiarities, and Python 2's [floor] division: there's a technical reason behind them that makes the language consistent on some level, but it produces counter-intuitive results to someone who's not familiar with how the language works under-the-hood.