[backlight.py] Added script to set backlight brightness using sysfs
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scripts/backlight.py
Executable file
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scripts/backlight.py
Executable file
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#!/usr/bin/env python3
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##############################################################################
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# backlight.py -- A script for setting the backlight brightness using sysfs. #
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# 2021 © Marcel Kapfer <opensource@mmk2410.org> #
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# Licensed unter the MIT/Expat License #
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# #
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# It is expected that the running user has permission to change the relevant #
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# sysfs file. See https://wiki.archlinux.org/title/Backlight#ACPI and the #
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# related "Discussion" wiki page on how to grant users the necessary right #
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##############################################################################
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import sys
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SYS_DIR = "/sys/class/backlight/"
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GRAPHICS_CARD = "intel_backlight"
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ACTUAL_BRIGHTNESS_FILE = "/actual_brightness"
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MAX_BRIGHTNESS_FILE = "/max_brightness"
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BRIGHTNESS_FILE = "/brightness"
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def __read_file_as_int(path: str, function: str) -> int:
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"""Read the value at the given `path` as integer.
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It is expected that the value in te file can be casted to an integer.
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Parameters
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----------
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path : str
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Path to the file to read.
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function : str
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Information about the reason for writing the file. Used only for better error messages.
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Returns
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-------
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int
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Value read at the file at `path`.
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"""
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try:
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with open(path, "r") as f:
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value = f.readline()
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except FileNotFoundError:
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print("[ERROR] Could not read {}. File {} not found.".format(function, path))
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sys.exit(2)
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except PermissionError:
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print("[ERROR] Could not read {}. Permission to read {} denied.".format(function, path))
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sys.exit(3)
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except IsADirectoryError:
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print("[ERROR] Could not read {}. {} is a directory.".format(function, path))
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sys.exit(4)
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try:
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value = int(value.strip())
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except ValueError:
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print("[ERROR] Could not parse {}.".format(function))
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sys.exit(1)
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return value
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def __write_int_as_file(path: str, value: int, function: str) -> None:
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"""Write the given integer `value` to the given `path`.
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This functions *overwrites* the file at `path`.
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Parameters
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----------
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path : str
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Path to the file to write.
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value : int
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Value to write the file at `path`.
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function : str
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Information about the reason for writing the file. Used only for better error messages.
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"""
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try:
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with open(path, "w") as f:
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print(value, file=f)
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except FileNotFoundError:
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print("[ERROR] Could not write {}. File {} not found".format(function, path))
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sys.exit(2)
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except PermissionError:
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print("[ERROR] Could not write {}. Permission to write {} denied.".format(function, path))
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sys.exit(3)
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except IsADirectoryError:
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print("[ERROR] Could not write {}. {} is a directory.".format(function, path))
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sys.exit(4)
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def actual_brightness() -> int:
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"""Get actual brightness value using sysfs.
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Read the actual brightness value from the corresponding file in sysfs.
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Returns
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-------
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int
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Actual brightness value.
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"""
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path = SYS_DIR + GRAPHICS_CARD + ACTUAL_BRIGHTNESS_FILE
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return __read_file_as_int(path, "actual brightness")
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def max_brightness() -> int:
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"""Get maximum brightness value using sysfs.
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Read the maximum brightness value from the corresponding file in sysfs.
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Returns
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-------
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int
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Maximum brightness value.
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"""
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path = SYS_DIR + GRAPHICS_CARD + MAX_BRIGHTNESS_FILE
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return __read_file_as_int(path, "maximal brightness")
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def set_brightness(value: int) -> None:
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"""Set a new brightness value using sysfs.
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Set the given brightness `value` by writing the the corresponding file in sysfs.
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Parameters
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----------
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value:
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New brightness value.
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"""
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path = SYS_DIR + GRAPHICS_CARD + BRIGHTNESS_FILE
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__write_int_as_file(path, value, "brightness")
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def safe_set_brightness(new_brightness: int, max_brightness_value: int) -> None:
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"""Set new brightness with obaying safety.
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Set a new brightness value using `set_brightness` by checking the value for some pitfalls.
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At the lower end the functions does not allow a brightness value lower than 5% of the maximum brightness.
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At the upper end the functions does not allow a brightness value higher than 100% of the maximum brightness.
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Parameters
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----------
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new_brightness : int
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Value to set as brightness.
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max_brightness_value : int
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Maximum brightness value.
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"""
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min_brightness_value = int(0.05 * max_brightness_value)
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if new_brightness < min_brightness_value:
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new_brightness = min_brightness_value
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elif new_brightness > max_brightness_value:
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new_brightness = max_brightness_value
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set_brightness(new_brightness)
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def calc_brightness(value: float, actual_brightness_value: int, max_brightness_value: int, function: str) -> int:
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"""Calculate brightness value based on actual and maximal brightness.
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The function calculates a brightness value using the `function` string and the `value` as a percentage.
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If `function` is empty the new brightness is the the `value` percentage of the maximum brightness.
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If `function` is + or - then the `value` percentage of the maximum brightness is added/subtracted from the actual brightness.
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Parameters
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----------
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value : float
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The wanted change as a percentage.
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actual_brightness_value : int
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Value of the actual brightness.
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max_brightness_value : int
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Value of the maximum brightness.
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function : str
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Either "+" for addition to actual brightness, "-" for substraction of actual brightness or "" for relative to maximum brightness.
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Returns
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-------
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int
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Calculated brightness value.
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"""
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if function == "+":
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new_brightness = actual_brightness_value + int(value * max_brightness_value)
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elif function == "-":
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new_brightness = actual_brightness_value - int(value * max_brightness_value)
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else:
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new_brightness = int(value * max_brightness_value)
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return new_brightness
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def parse_arg(arg: str) -> (int, str):
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"""Parse argument and return value and modifier.
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It is expected that the passed argument is the unaltered CLI argument of the form [+/-]NUMBER%.
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The function will check the format and raise a `ValueError` if it is not compatible.
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Parameters
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----------
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arg : str
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String to parse
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Returns
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-------
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int
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Parsed value
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mod
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Parsed modifier, either +, - or an empty string.
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Raises
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------
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ValueError
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If given argument has not the required format.
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"""
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if len(arg) < 2 or len(arg) > 5:
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raise ValueError("Wrong format. Expected lenght between 2 and 5 characters")
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if arg[-1] != "%":
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raise ValueError("Wrong format. Expected '%' at the end.")
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mod = arg[0]
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number_start_index = 0
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if mod == "+" or mod == "-":
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number_start_index = 1
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else:
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try:
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int(mod)
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except ValueError:
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raise ValueError("Wrong format. Modifier neither +/- nor value of type integer.")
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# Set modifier to empty string to return a halfway meaningful value.
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mod = ""
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try:
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value = 0.01 * int(arg[number_start_index:-1])
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except ValueError:
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raise ValueError("Wrong format. Supplied value not a integer.")
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return value, mod
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def print_help() -> None:
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"""Print help on using this script."""
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print("Usage:")
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print("backlight.py [+/-]NUMBER%")
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print(" +: Increase brightness by NUMBER%")
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print(" -: Decrease brightness by NUMBER%")
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print(" : Set brightness to NUMBER%")
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def main():
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"""Main entry point."""
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if len(sys.argv) != 2:
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print("[ERROR] Unexpected amount of arguments.")
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print_help()
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sys.exit(5)
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try:
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value, mod = parse_arg(sys.argv[1])
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except ValueError:
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print("[ERROR] Malformed argument.")
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print_help()
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sys.exit(6)
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actual_brightness_value = actual_brightness()
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max_brightness_value = max_brightness()
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new_brightness = calc_brightness(value, actual_brightness_value, max_brightness_value, mod)
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safe_set_brightness(new_brightness, max_brightness_value)
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if __name__ == "__main__":
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main()
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