flake8-tkinter

A flake8 plugin that helps you write better Tkinter code

Project idea by @insolor

Installation

pip install flake8-tkinter

List of warnings

Common mistakes

• TK102: Using multiple mainloop calls is unnecessary. One call is perfectly enough. (example)
• TK111: Calling callback_handler() instead of passing the reference for on-click or binding callback. (example)
• TK112: Calling callback_handler() with arguments instead of passing the reference for on-click or binding callback. If you need to call callback_handler with arguments, use lambda or functools.partial. (example)
• TK131: Assigning result of geometry manager call to a variable. (example)

Best practices

• TK141: Using bind without add=True will overwrite any existing bindings to this sequence on this widget. Either overwrite them explicitly with add=False or use add=True to keep existing bindings. (example)
• TK142: Creating tag bindings in a loop can lead to memory leaks. Store the returned command names in a list to clean them up later. (example)
• TK201: Using from tkinter import * is generally a bad practice and discouraged. Use import tkinter as tk or simply import tkinter instead. (example)
• TK202: Using from tkinter.ttk import * is generally a bad practice and discouraged. Use from tkinter import ttk instead. (example)
• TK211: Using import tkinter.ttk as ttk is pointless. Use from tkinter import ttk instead. (example)
• TK221: Using tkinter.TRUE, tkinter.FALSE, etc. is pointless. Use an appropriate Python boolean instead. (example)
• TK251: Using tkinter.Message widget. It's redundant since tkinter.Label provides the same functionality. (example)

Code quality

• TK304: Value for add in bind methods should be a boolean. (example)

Opinionated warnings

• TK504: Using a tkinter constant. Use a string literal instead (disabled by default). (example)

Examples

TK102

# Bad
def foo():
    top = tk.Toplevel()
    ...
    top.mainloop()

root.mainloop()

# Good
def foo():
    top = tk.Toplevel()
    ...
    
root.mainloop()

TK111

# Bad
tk.Button(..., command=foo())
button.config(command=bar())
button.bind("<Button-3>", baz())

# Good
tk.Button(..., command=foo)
button.config(command=bar)
button.bind("<Button-3>", baz)

TK112

# Bad
tk.Button(..., command=foo(arg, kwarg=...))
button.config(command=bar(arg, kwarg=...))
button.bind("<Button-3>", baz(arg, kwarg=...))

# Good
tk.Button(..., command=lambda: foo(arg, kwarg=...))
button.config(command=lambda: bar(arg, kwarg=...))
button.bind("<Button-3>", lambda e: baz(arg, kwarg=...))

TK131

# Bad
btn = tk.Button().grid()

# Good
btn = tk.Button()
btn.grid()

TK201

# Bad
from tkinter import *

# Good
import tkinter
# OR
import tkinter as tk

TK202

# Bad
from tkinter.ttk import *

# Good
from tkinter import ttk

TK211

# Bad
import tkinter.ttk as ttk

# Good
from tkinter import ttk

TK221

# Bad
w.pack(expand=tk.TRUE)
w.pack(expand=tk.FALSE)
w.pack(expand=tk.YES)
w.pack(expand=tk.NO)
w.pack(expand=tk.ON)
w.pack(expand=tk.OFF)

# Good
w.pack(expand=True)
w.pack(expand=False)

TK141

# Bad
w.bind("<Button-1>", foo)

# Good
w.bind("<Button-1>", foo, add=True)
# OR
w.bind("<Button-1>", foo, add=False)

TK142

# Bad
for index, foo in enumerate(foos):
    w.tag_bind(f"bar_{index}", "<Button-1>", baz)
    
# Good
for index, foo in enumerate(foos):
    tcl_command = w.tag_bind(f"bar_{index}", "<Button-1>", baz)
    bindings.append(tcl_command)  # Clean them up later with `.deletecommand()`

TK251

_Yes, there's some minor diffrence in text wrapping, but that can be easily fixed

# Bad
w = tkinter.Message()

# Good
w = tkinter.Label()

TK304

# Bad
w.bind("<Button-1>", foo, add="+")

# Good
w.bind("<Button-1>", foo, add=True)

TK504

# Bad
w.pack(side=tkinter.BOTTOM, fill=tkinter.BOTH)

# Good
w.pack(side="bottom", fill="both")

Planned warnings

• Common mistakes (TK101-TK179)

  • TK101: Using multiple tkinter.Tk instances. Child windows must be created from tkinter.Toplevel.
  • TK103: Suggest refactoring code that uses .update(), as it's usually pointless, potentially harmful, and considered a code smell.
  • TK113: Callback handler should be a callable
  • TK121: Using time.sleep() in tkinter code. Use .after() in some form instead.
  • TK122: Using an infinite loop in callback handler. Propose to use recursive function with .after().
  • TK???: Suggest keeping reference of local PhotoImage instance to avoid GC.
  • TK151: Don't use w.setup() directly. Use init args, or w.configure().
  • Extend TK111 and Tk112 to check in w.after() calls.

• Cross platform (TK181-TK199)

  • TK181: Using <MouseWheel> binding. It doesn't work on Linux with Tk 8.6 (use button4-5 instead)
  • TK182: Using <Shift-Tab> binding. It doesn't work on Linux (use <ISO_Left_Tab> instead)
  • TK183: Using <Menu> binding. It doesn't work on Windows (use <App> instead)
  • TK184: Binding to control or alt with constant values. It probably won't work on macOS.
  • TK191: Not calling wait_visibility before wm_attributes("-alpha").
  • TK192: Using w.state("zoomed"). It throws an error on Linux (and on mac too?). Use wm_attributes("-zoomed", True)

• Best practices (TK201-TK299)

  • TK222: Using tk.N+tk.S+tk.E+tk.W and combinations like that. Use tk.NSEW, or some other constant instead.
  • TK241: Creating a widget without parent specified, and there is a container in the same scope.
  • TK252: Using tkinter.Menu without tearoff=False
  • TK261: Using subsequent wm_attributes calls. It can take value pairs.

• Code quality (TK301-TK399)

  • TK301: Suggest using more clear binding sequences, like <Button-1> instead of <1> and <Key-a> instead of <a>.
  • TK302: Suggest using more clear tkinter.Text indexes, like end - 1 chars instead of end-1c.
  • TK303: Using a float as tkinter.Text index. It works because how Tkinter translates Python objects to Tcl, but it shouldn't.

• OO (TK401-TK499)

  • TK401: Consider refactoring a huge app with OOP.
  • TK402: Consider refactoring widget into separate class.

• Opinionated rules (TK501-TK599)

  • TK501: Calling mainloop() on something other than the root window.
  • TK502: Using things like root.wm_title(). Use root.title(). (But there should be exceptions, like wm_attributes, and instead warn on plain attributes)
  • TK503: Using subscripting for widget cget and configure. Use .cget() and .configure() instead.

Development

1. Clone the repo
2. Set up a virtual environment, activate, and install flake8 and pytest in it
3. Run pip install -e . to install flake8-tkinter in editable format
4. Run python3 -m pytest to test your changes