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import os

def list_pids():
    pids = []
    for entry in os.listdir('/proc'):
        if entry.isdigit():
            pids.append(int(entry))
    return sorted(pids)

if __name__ == '__main__':
    print(list_pids()[:10])

def read_status(pid: int) -> dict:
    path = f'/proc/{pid}/status'
    info = {}
    try:
        with open(path, 'r') as f:
            for line in f:
                key, _, value = line.partition(':')
                info[key.strip()] = value.strip()
    except (FileNotFoundError, ProcessLookupError):
        return {}
    return info

def get_process_summary(pid: int) -> dict:
    info = read_status(pid)
    if not info:
        return None
    return {
        'pid': pid,
        'name': info.get('Name', '?'),
        'state': info.get('State', '?'),
        'rss_kb': int(info.get('VmRSS', '0 kB').split()[0]),
    }

CLK_TCK = os.sysconf('SC_CLK_TCK')  # 보통 100 (1틱 = 10ms)

def read_cpu_time(pid: int) -> float:
    path = f'/proc/{pid}/stat'
    try:
        with open(path, 'r') as f:
            raw = f.read()
    except (FileNotFoundError, ProcessLookupError):
        return 0.0

    # comm 필드는 '(name)' 형태이며 공백을 포함할 수 있으므로
    # 마지막 ')'를 기준으로 앞뒤를 분리한다.
    rest = raw[raw.rfind(')') + 2:]
    fields = rest.split()

    # rest는 state(3번째 필드)부터 시작하므로 인덱스가 3만큼 밀린다.
    # utime은 원래 14번째 필드 -> fields[14-3] = fields[11]
    utime = int(fields[11])
    stime = int(fields[12])
    return (utime + stime) / CLK_TCK

def read_meminfo() -> dict:
    info = {}
    with open('/proc/meminfo', 'r') as f:
        for line in f:
            key, _, value = line.partition(':')
            info[key.strip()] = int(value.split()[0])  # kB 단위
    return info

def memory_usage_percent() -> float:
    mem = read_meminfo()
    total = mem['MemTotal']
    available = mem['MemAvailable']
    used = total - available
    return used / total * 100

def top_memory_processes(n: int = 5) -> list:
    results = []
    for pid in list_pids():
        summary = get_process_summary(pid)
        if summary:
            results.append(summary)
    results.sort(key=lambda p: p['rss_kb'], reverse=True)
    return results[:n]

if __name__ == '__main__':
    print(f'시스템 메모리 사용률: {memory_usage_percent():.1f}%')
    for proc in top_memory_processes():
        print(f'{proc["pid"]:>7}  {proc["rss_kb"]:>10} kB  {proc["name"]}')

def read_cmdline(pid: int) -> list:
    path = f'/proc/{pid}/cmdline'
    try:
        with open(path, 'rb') as f:
            raw = f.read()
    except (FileNotFoundError, ProcessLookupError):
        return []
    # 인자는 NULL 바이트로 구분되며 마지막에 빈 문자열이 남을 수 있다.
    return [arg for arg in raw.decode(errors='replace').split('\x00') if arg]

def count_open_fds(pid: int) -> int:
    path = f'/proc/{pid}/fd'
    try:
        return len(os.listdir(path))
    except (FileNotFoundError, PermissionError):
        return -1