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STATUS_FILENAME = "/var/lib/dpkg/status"

def iter_packages():
    """The main function of module."""
    info = []
    with open(STATUS_FILENAME) as infofile:
        for line in infofile:
            if line.startswith(' '):
                # continue content
                info[-1][-1] += '\n' + line[1:].rstrip()
            elif not line.strip():
                # end of block
                if info:
                    yield dict(info)
                info = []
            else:
                key, content = line.split(":", 1)
                info.append([key, content.strip()])
        if info:
            yield dict(info)
            
def package_exists(package_name):
    """This function checks if package exists."""
    return any(info["Package"] == package_name
        for info in iter_packages())

def get_package(package_name):
    """Returns all values of a package in a dictionary."""
    for info in iter_packages():
        if info["Package"] == package_name:
            return info
    raise KeyError("The package does not exist")

def list_package_names():
    """Returns all package names."""
    return [
        info["Package"]
        for info in iter_packages()
    ]

def count_packages():
    """Counts all installed packages."""
    return sum(1 for info in iter_packages())

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"""
The module provides information about installed debian packages.
The module can only be executed if the operating system supports debian packages!
"""
STATUS_FILENAME = "/var/lib/dpkg/status"
__author__ = "Ben Fässler <faesslerben@gmail.com>"
__license__ = "MIT"
__all__ = ["iter_packages (not for user)",
           "package_exists",
           "get_package",
           "list_package_names",
           "count_packages"
        ]
__version__ = "0.0.1"

import os

if not os.path.exists(STATUS_FILENAME):
    raise FileNotFoundError("The information file was not found! Without this file, the module can not be executed!")
del os

def iter_packages():
    """The main function of module."""
    info = []
    with open(STATUS_FILENAME) as infofile:
        for line in infofile:
            if line.startswith(' '):
                # continue content
                info[-1][-1] += '\n' + line[1:].rstrip()
            elif not line.strip():
                # end of block
                if info:
                    yield dict(info)
                info = []
            else:
                key, content = line.split(":", 1)
                info.append([key, content.strip()])
        if info:
            yield dict(info)
            
def package_exists(package_name):
    """This function checks if package exists.
Arguments:
    package_name - The name of the package
    """
    return any(info["Package"] == package_name
        for info in iter_packages())

def get_package(package_name):
    """Returns all values of a package in a dictionary.
Arguments:
    package_name - The name of the package
    """
    for info in iter_packages():
        if info["Package"] == package_name:
            return info
    raise KeyError("The package does not exist")

def list_package_names():
    """Returns all package names."""
    return [
        info["Package"]
        for info in iter_packages()
    ]

def count_packages():
    """Counts all installed packages."""
    return sum(1 for info in iter_packages())

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Auf Modulebene sollte so wenig wie möglich passieren

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if not os.path.exists(STATUS_FILENAME):
    raise FileNotFoundError("The information file was not found! Without this file, the module can not be executed!")
else:
    if not os.access(STATUS_FILENAME, os.R_OK):
        raise PermissionError("No reading rights for the information file! Without this file, the module can not be executed!")

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if __name__ == "__main__":

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def print_documentation():
    for i, a in zip([iter_packages, package_exists, get_package_values, list_package_names, count_packages], __all__):
        print(a)
        print("____________________")
        print(i.__doc__ + "\n")

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iter_packages (not for user)
____________________
The main function of module.
    

package_exists
____________________
This function checks if package exists.
Arguments:
    package_name - The name of the package
The function returns True or False.
    

get_package_values
____________________
Returns all values of a package in a dictionary.
Arguments:
    package_name - The name of the package
    

list_package_names
____________________
Returns all names of installed packages.
The function returns the names in a list.
    

count_packages
____________________
Counts all installed packages.
The function returns the number as an integer.

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def package_created_paths(package_name):
    """Returns files and folders created by the package as a path.
Arguments:
    package_name - The name of the package
The function returns the paths in a list.
    """
    paths = []
    filename = package_name + ".md5sums"
    with open(pathlib.PurePath("/var/lib/dpkg/info", filename)) as infofile:
        for info in infofile:
            paths.append(info.split("  ")[1].strip())
        return paths

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Die Einrückung vom Docstring stimmt nicht

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Wobei Dein Stil noch geringfügig abweicht. Ich weiss nicht ob das '-' statt des ':' bei den Argumenten erkannt wird.