Parameters step notation in python

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Parameters step notation in python

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#1 by (0 votes)

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Hello the following code fragment belongs to tkinter python, however I find a step notation of parameters that I can not find in the documentation. You can offer me help. The syntax is the following config (text = format% args) and the context is as follows.

class StatusBar(Frame):

    def __init__(self, master):
        Frame.__init__(self, master)
        self.label = Label(self, bd=1, relief=SUNKEN, anchor=W)
        self.label.pack(fill=X)

    def set(self, format, *args):
        self.label.config(text=format % args)
        self.label.update_idletasks()

    def clear(self):
        self.label.config(text="")
        self.label.update_idletasks()

python tkinter

asked by Silver137 31.08.2018 в 16:21

source

1 answer

Filter items from FormArray Script to convert .P12 to .CER

score 0 · Accepted Answer

The set method only uses the old string formatting method using % to assign the string to be displayed by the Label , which follows the syntax:

% values format

where formato is the string to be formatted, which contains one or more specifiers to be replaced that are identified by the character "%" at the beginning of it, while valores can be a single element or a tuple of items with the same number of items specified in the format or a mapping object, such as a dictionary. You can see a much more detailed explanation in the documentation:

String formating operations

Some examples:

>>> "Un rectángulo de %.2f cm de ancho por %.2f cm de alto" % (4.2555, 8.2146)
'Un rectángulo de 4.26 cm de ancho por 8.21 cm de alto'

>>> "Stack Overlow en %s" % "español" 
'Stack Overlow en español'

>>> '%(nombre)s tiene %(edad)d años' % {"nombre": "Pedro", "edad": 27}
'Pedro tiene 27 años'

Currently this method is still available but is considered outdated in favor of str.format and the formatted string literals (Python > = 3.6) both considerably more flexible.

You also have an extensive explanation with examples included in the documentation:

Format string syntax

In your case the method expects a string to be formatted as the first argument and an indeterminate number of positional arguments that will correspond exactly to the values to be replaced in the string. A reproducible example so you can see it with some different examples of method call:

import tkinter as tk


class StatusBar(tk.Frame):

    def __init__(self, master):
        tk.Frame.__init__(self, master)
        self.label = tk.Label(self, bd=1, relief=tk.SUNKEN, anchor=tk.W)
        self.label.pack(fill=tk.X)

    def set_string(self, format_, *args):
        self.label.config(text=format_ % args)
        self.label.update_idletasks()

    def clear(self):
        self.label.config(text="")
        self.label.update_idletasks()


if __name__ == "__main__":
    root = tk.Tk()
    root.geometry("400x200")

    f1 = StatusBar(root)
    f1.set_string("%.2f, %.2f", 4.257, 2.356)
    f1.pack(fill=tk.X)

    f2 = StatusBar(root)
    f2.set_string("%s, %s y %s", "Pedro", "Laura", "Marco")
    f2.pack(fill=tk.X)

    f3 = StatusBar(root)
    f3.set_string("%30s", "Stack Overflow")
    f3.pack(fill=tk.X)

    f4 = StatusBar(root)
    a = 2
    b = 3
    r = 6
    op = "x"
    f4.set_string("%d %s %d = %d", a, op, b, r)
    f4.pack(fill=tk.X)

    root.mainloop()

Note: Avoid using set and format as names for our methods or variables, both functions are prebuilt in Python, which overlap with it, apart from being confusing .

*args is used to send an indeterminate number of arguments ("non-keywords") to the function, so that at the end args will be a tuple that will contain the values of those arguments and whose length is only known at run time when the function is called. This is so, because the number of arguments of the function depends on the number of specifiers to be substituted in the chain passed as the first argument, as seen in the previous example.