Draft utility to figure out what are the primary dependencies of a Python package. Let's list modules that are imported in the code (ignore stdlib and internals).

depends.py

#!/usr/bin/env python
# -*- coding: UTF-8 -*-
"""Helps you maintain ``install_requires``."""


#: List of modules in standard library.
#: See https://docs.python.org/3/py-modindex.html
PY3_MODULES = [
    '__future__',
    '__main__',
    '_dummy_thread',
    '_thread',
    'abc',
    'aifc',
    'argparse',
    'array',
    'ast',
    'asynchat',
    'asyncio',
    'asyncore',
    'atexit',
    'audioop',
    'base64',
    'bdb',
    'binascii',
    'binhex',
    'bisect',
    'builtins',
    'bz2',
    'calendar',
    'cgi',
    'cgitb',
    'chunk',
    'cmath',
    'cmd',
    'code',
    'codecs',
    'codeop',
    'collections',
    'colorsys',
    'compileall',
    'concurrent',
    'configparser',
    'contextlib',
    'copy',
    'copyreg',
    'cProfile',
    'crypt',
    'csv',
    'ctypes',
    'curses',
    'datetime',
    'dbm',
    'decimal',
    'difflib',
    'dis',
    'distutils',
    'doctest',
    'dummy_threading',
    'email',
    'encodings',
    'ensurepip',
    'enum',
    'errno',
    'faulthandler',
    'fcntl',
    'filecmp',
    'fileinput',
    'fnmatch',
    'formatter',
    'fpectl',
    'fractions',
    'ftplib',
    'functools',
    'gc',
    'getopt',
    'getpass',
    'gettext',
    'glob',
    'grp',
    'gzip',
    'hashlib',
    'heapq',
    'hmac',
    'html',
    'http',
    'imaplib',
    'imghdr',
    'imp',
    'importlib',
    'inspect',
    'io',
    'ipaddress',
    'itertools',
    'json',
    'keyword',
    'lib2to3',
    'linecache',
    'locale',
    'logging',
    'lzma',
    'macpath',
    'mailbox',
    'mailcap',
    'marshal',
    'math',
    'mimetypes',
    'mmap',
    'modulefinder',
    'msilib',
    'msvcrt',
    'multiprocessing',
    'netrc',
    'nis',
    'nntplib',
    'numbers',
    'operator',
    'optparse',
    'os',
    'ossaudiodev',
    'parser',
    'pathlib',
    'pdb',
    'pickle',
    'pickletools',
    'pipes',
    'pkgutil',
    'platform',
    'plistlib',
    'poplib',
    'posix',
    'pprint',
    'profile',
    'pstats',
    'pty',
    'pwd',
    'py_compile',
    'pyclbr',
    'pydoc',
    'queue',
    'quopri',
    'random',
    're',
    'readline',
    'reprlib',
    'resource',
    'rlcompleter',
    'runpy',
    'sched',
    'select',
    'selectors',
    'shelve',
    'shlex',
    'shutil',
    'signal',
    'site',
    'smtpd',
    'smtplib',
    'sndhdr',
    'socket',
    'socketserver',
    'spwd',
    'sqlite3',
    'ssl',
    'stat',
    'statistics',
    'string',
    'stringprep',
    'struct',
    'subprocess',
    'sunau',
    'symbol',
    'symtable',
    'sys',
    'sysconfig',
    'syslog',
    'tabnanny',
    'tarfile',
    'telnetlib',
    'tempfile',
    'termios',
    'test',
    'textwrap',
    'threading',
    'time',
    'timeit',
    'tkinter',
    'token',
    'tokenize',
    'trace',
    'traceback',
    'tracemalloc',
    'tty',
    'turtle',
    'turtledemo',
    'types',
    'unicodedata',
    'unittest',
    'urllib',
    'uu',
    'uuid',
    'venv',
    'warnings',
    'wave',
    'weakref',
    'webbrowser',
    'winreg',
    'winsound',
    'wsgiref',
    'xdrlib',
    'xml',
    'xmlrpc',
    'zipfile',
    'zipimport',
    'zlib',
]
#: List of modules in standard library.
#: See https://docs.python.org/2/py-modindex.html
PY2_MODULES = [
    '__builtin__',
    '__future__',
    '__main__',
    '_winreg',
    'abc',
    'aepack',
    'aetools',
    'aetypes',
    'aifc',
    'al',
    'AL',
    'anydbm',
    'applesingle',
    'argparse',
    'array',
    'ast',
    'asynchat',
    'asyncore',
    'atexit',
    'audioop',
    'autoGIL',
    'base64',
    'BaseHTTPServer',
    'Bastion',
    'bdb',
    'binascii',
    'binhex',
    'bisect',
    'bsddb',
    'buildtools',
    'bz2',
    'calendar',
    'Carbon',
    'cd',
    'cfmfile',
    'cgi',
    'CGIHTTPServer',
    'cgitb',
    'chunk',
    'cmath',
    'cmd',
    'code',
    'codecs',
    'codeop',
    'collections',
    'ColorPicker',
    'colorsys',
    'commands',
    'compileall',
    'compiler',
    'ConfigParser',
    'contextlib',
    'Cookie',
    'cookielib',
    'copy',
    'copy_reg',
    'cPickle',
    'cProfile',
    'crypt',
    'cStringIO',
    'csv',
    'ctypes',
    'curses',
    'datetime',
    'dbhash',
    'dbm',
    'decimal',
    'DEVICE',
    'difflib',
    'dircache',
    'dis',
    'distutils',
    'dl',
    'doctest',
    'DocXMLRPCServer',
    'dumbdbm',
    'dummy_thread',
    'dummy_threading',
    'EasyDialogs',
    'email',
    'encodings',
    'ensurepip',
    'errno',
    'exceptions',
    'fcntl',
    'filecmp',
    'fileinput',
    'findertools',
    'FL',
    'fl',
    'flp',
    'fm',
    'fnmatch',
    'formatter',
    'fpectl',
    'fpformat',
    'fractions',
    'FrameWork',
    'ftplib',
    'functools',
    'future_builtins ',
    'gc',
    'gdbm',
    'gensuitemodule',
    'getopt',
    'getpass',
    'gettext',
    'gl',
    'GL',
    'glob',
    'grp',
    'gzip',
    'hashlib',
    'heapq',
    'hmac',
    'hotshot',
    'htmlentitydefs',
    'htmllib',
    'HTMLParser',
    'httplib',
    'ic',
    'icopen',
    'imageop',
    'imaplib',
    'imgfile',
    'imghdr',
    'imp',
    'importlib',
    'imputil',
    'inspect',
    'io',
    'itertools',
    'jpeg',
    'json',
    'keyword',
    'lib2to3',
    'linecache',
    'locale',
    'logging',
    'macerrors',
    'MacOS',
    'macostools',
    'macpath',
    'macresource',
    'mailbox',
    'mailcap',
    'marshal',
    'math',
    'md5',
    'mhlib',
    'mimetools',
    'mimetypes',
    'MimeWriter',
    'mimify',
    'MiniAEFrame',
    'mmap',
    'modulefinder',
    'msilib',
    'msvcrt',
    'multifile',
    'multiprocessing',
    'mutex',
    'Nav',
    'netrc',
    'new',
    'nis',
    'nntplib',
    'numbers',
    'operator',
    'optparse',
    'os',
    'ossaudiodev',
    'parser',
    'pdb',
    'pickle',
    'pickletools',
    'pipes',
    'PixMapWrapper',
    'pkgutil',
    'platform',
    'plistlib',
    'popen2',
    'poplib',
    'posix',
    'posixfile',
    'pprint',
    'profile',
    'pstats',
    'pty',
    'pwd',
    'py_compile',
    'pyclbr',
    'pydoc',
    'Queue',
    'quopri',
    'random',
    're',
    'readline',
    'resource',
    'rexec',
    'rfc822',
    'rlcompleter',
    'robotparser',
    'runpy',
    'sched',
    'ScrolledText',
    'select',
    'sets',
    'sgmllib',
    'sha',
    'shelve',
    'shlex',
    'shutil',
    'signal',
    'SimpleHTTPServer',
    'SimpleXMLRPCServer',
    'site',
    'smtpd',
    'smtplib',
    'sndhdr',
    'socket',
    'SocketServer',
    'spwd',
    'sqlite3',
    'ssl',
    'stat',
    'statvfs',
    'string',
    'StringIO',
    'stringprep',
    'struct',
    'subprocess',
    'sunau',
    'sunaudiodev',
    'SUNAUDIODEV',
    'symbol',
    'symtable',
    'sys',
    'sysconfig',
    'syslog',
    'tabnanny',
    'tarfile',
    'telnetlib',
    'tempfile',
    'termios',
    'test',
    'textwrap',
    'thread',
    'threading',
    'time',
    'timeit',
    'Tix',
    'Tkinter',
    'token',
    'tokenize',
    'trace',
    'traceback',
    'ttk',
    'tty',
    'turtle',
    'types',
    'unicodedata',
    'unittest',
    'urllib',
    'urllib2',
    'urlparse',
    'user',
    'UserDict',
    'UserList',
    'UserString',
    'uu',
    'uuid',
    'videoreader',
    'W',
    'warnings',
    'wave',
    'weakref',
    'webbrowser',
    'whichdb',
    'winsound',
    'wsgiref',
    'xdrlib',
    'xml',
    'xmlrpclib',
    'zipfile',
    'zipimport',
    'zlib',
]


import argparse
import os
import re


IMPORT_REGEXP = re.compile(r'^[\s]*(from [\w._]+ |)import ([\w._, ]+)')


def is_dependency(module, root_module=None):
    """Return ``True`` if ``module`` implies external dependency."""
    if not module:
        return False
    if module.startswith('.'):
        return False
    if re.match(r'^{0}(\.\w+)?$'.format(root_module), module):
        return False
    if module in PY2_MODULES:
        return False
    return True


def root_module(module):
    """Return only root package in module name."""
    module = module.split(' ')[0]
    parts = module.split('.')
    return parts[0]


def modules_in_import_line(line):
    """Yield modules in import statement."""
    line = line.lstrip()
    if line.startswith('import '):
        line = line[len('import '):]
        matches = re.findall(r'([\w._]+( as [\w_]+)?)', line)
        for match in matches:
            yield root_module(match[0])
    elif line.startswith('from '):
        line = line[len('from '):]
        match = re.match(r'([\w._]+)', line)
        if match:
            yield root_module(match.group(0))


def imports_in_file(lines):
    """Yield import statements in ``lines``."""
    for line in lines:
        match = re.match(IMPORT_REGEXP, line)
        if match:
            for module in modules_in_import_line(match.group(0)):
                yield module


def python_files(path):
    """Yield path of Python scripts in path."""
    for (dirpath, dirnames, filenames) in os.walk(path):
        for filename in filenames:
            if filename.endswith('.py'):
                yield dirpath + "/" + filename


def main(args=None):
    parser = argparse.ArgumentParser(
        description='Show source code dependencies.')
    parser.add_argument(
        'source',
        type=str,
        help='an integer for the accumulator')
    args = parser.parse_args()
    root_module = os.path.basename(args.source)
    root_path = args.source
    modules = set()
    for filename in python_files(root_path):
        with open(filename) as lines:
            for module in imports_in_file(lines):
                modules.add(module)
    for module in sorted(modules):
        if is_dependency(module, root_module):
            print module


if __name__ == '__main__':
    main()