在Python中处理单值元组的最佳实践是什么?

如果是字符串或元组,您需要以某种方式测试类型。我会这样做:

keywords = library.get_keywords()
if not isinstance(keywords, tuple):
    keywords = (keywords,) # Note the comma
for keyword in keywords:
    do_your_thang(keyword)

对于您的第一个问题,我不确定这是否是最佳答案,但我认为您需要检查自己返回的值是字符串还是元组,并相应地进行操作。

对于第二个问题,任何变量都可以通过放置 , 旁边:

>>> x='abc'
>>> x
'abc'
>>> tpl=x,
>>> tpl
('abc',)

把这两个想法放在一起:

>>> def make_tuple(k):
...     if isinstance(k,tuple):
...             return k
...     else:
...             return k,
... 
>>> make_tuple('xyz')
('xyz',)
>>> make_tuple(('abc','xyz'))
('abc', 'xyz')

注意:imho使用isInstance或任何其他形式的逻辑在运行时需要检查对象类型通常是一个坏主意。但对于这个问题,我看不出任何解决办法。

你的 tuple_maker 不会像你想象的那样。一个等价的定义 tuple maker 对你来说是

def tuple_maker(input):
    return input

你看到的是 tuple_maker("a string") 返回字符串,而 tuple_maker(["str1","str2","str3"]) 返回字符串列表;两者都不返回元组!

python中的元组是由逗号而不是括号来定义的。因此 (1,2) 是包含值的元组 1 和 2 ,同时 (1,) 是包含单个值的元组 一 .

如其他人指出的,要将值转换为元组,请使用 tuple .

>>> tuple([1])
(1,)
>>> tuple([1,2])
(1,2)

总是有蒙凯补丁!

# Store a reference to the real library function
really_get_keywords = library.get_keywords

# Define out patched version of the function, which uses the real
# version above, adjusting its return value as necessary
def patched_get_keywords():
    """Make sure we always get a tuple of keywords."""
    result = really_get_keywords()
    return result if isinstance(result, tuple) else (result,)

# Install the patched version
library.get_keywords = patched_get_keywords

注: 这个密码可能会烧毁你的房子和你的妻子睡觉。

我不检查长度为1,而是使用isInstance内置的。

>>> isinstance('a_str', tuple)
False
>>> isinstance(('str1', 'str2', 'str3'), tuple)
True

它是否绝对有必要返回元组,或者任何iterable都会这样做?

import collections
def iterate(keywords):
    if not isinstance(keywords, collections.Iterable):
        yield keywords
    else:
        for keyword in keywords:
            yield keyword


for keyword in iterate(library.get_keywords()):
    print keyword

对于第一个问题,可以使用

type(r) is tuple
#alternative
isinstance(r, tuple)
# one-liner
def as_tuple(r): return [ tuple([r]), r ][type(r) is tuple]

我喜欢用的第二件事 tuple([1]) . 认为这是一个品味问题。例如,还可以编写包装器 def tuple1(s): return tuple([s])

当使用tuple()构造函数方法而不是用于创建单个字符串tuple的默认类型定义时,需要注意一件重要的事情。下面是一个nose2/unittest脚本,您可以使用它来处理问题:

#!/usr/bin/env python
# vim: ts=4 sw=4 sts=4 et
from __future__ import print_function
# global
import unittest
import os
import sys
import logging
import pprint
import shutil

# module-level logger
logger = logging.getLogger(__name__)

# module-global test-specific imports
# where to put test output data for compare.
testdatadir = os.path.join('.', 'test', 'test_data')
rawdata_dir = os.path.join(os.path.expanduser('~'), 'Downloads')
testfiles = (
    'bogus.data',
)
purge_results = False
output_dir = os.path.join('test_data', 'example_out')


def cleanPath(path):
    '''cleanPath
    Recursively removes everything below a path

    :param path:
    the path to clean
    '''
    for root, dirs, files in os.walk(path):
        for fn in files:
            logger.debug('removing {}'.format(fn))
            os.unlink(os.path.join(root, fn))
        for dn in dirs:
            # recursive
            try:
                logger.debug('recursive del {}'.format(dn))
                shutil.rmtree(os.path.join(root, dn))
            except Exception:
                # for now, halt on all.  Override with shutil onerror
                # callback and ignore_errors.
                raise


class TestChangeMe(unittest.TestCase):
    '''
        TestChangeMe
    '''
    testdatadir = None
    rawdata_dir = None
    testfiles   = None
    output_dir  = output_dir

    def __init__(self, *args, **kwargs):
        self.testdatadir = os.path.join(os.path.dirname(
            os.path.abspath(__file__)), testdatadir)
        super(TestChangeMe, self).__init__(*args, **kwargs)
        # check for kwargs
        # this allows test control by instance
        self.testdatadir = kwargs.get('testdatadir', testdatadir)
        self.rawdata_dir = kwargs.get('rawdata_dir', rawdata_dir)
        self.testfiles = kwargs.get('testfiles', testfiles)
        self.output_dir = kwargs.get('output_dir', output_dir)

    def setUp(self):
        '''setUp
        pre-test setup called before each test
        '''
        logging.debug('setUp')
        if not os.path.exists(self.testdatadir):
            os.mkdir(self.testdatadir)
        else:
            self.assertTrue(os.path.isdir(self.testdatadir))
        self.assertTrue(os.path.exists(self.testdatadir))
        cleanPath(self.output_dir)

    def tearDown(self):
        '''tearDown
        post-test cleanup, if required
        '''
        logging.debug('tearDown')
        if purge_results:
            cleanPath(self.output_dir)

    def tupe_as_arg(self, tuple1, tuple2, tuple3, tuple4):
        '''test_something_0
            auto-run tests sorted by ascending alpha
        '''
        # for testing, recreate strings and lens
        string1 = 'string number 1'
        len_s1 = len(string1)
        string2 = 'string number 2'
        len_s2 = len(string2)
        # run the same tests...
        # should test as type = string
        self.assertTrue(type(tuple1) == str)
        self.assertFalse(type(tuple1) == tuple)
        self.assertEqual(len_s1, len_s2, len(tuple1))
        self.assertEqual(len(tuple2), 1)
        # this will fail
        # self.assertEqual(len(tuple4), 1)
        self.assertEqual(len(tuple3), 2)
        self.assertTrue(type(string1) == str)
        self.assertTrue(type(string2) == str)
        self.assertTrue(string1 == tuple1)
        # should test as type == tuple
        self.assertTrue(type(tuple2) == tuple)
        self.assertTrue(type(tuple4) == tuple)
        self.assertFalse(type(tuple1) == type(tuple2))
        self.assertFalse(type(tuple1) == type(tuple4))
        # this will fail
        # self.assertFalse(len(tuple4) == len(tuple1))
        self.assertFalse(len(tuple2) == len(tuple1))

    def default_test(self):
        '''testFileDetection
        Tests all data files for type and compares the results to the current
        stored results.
        '''
        # test 1
        __import__('pudb').set_trace()
        string1 = 'string number 1'
        len_s1 = len(string1)
        string2 = 'string number 2'
        len_s2 = len(string2)
        tuple1 = (string1)
        tuple2 = (string1,)
        tuple3 = (string1, string2)
        tuple4 = tuple(string1,)
        # should test as type = string
        self.assertTrue(type(tuple1) == str)
        self.assertFalse(type(tuple1) == tuple)
        self.assertEqual(len_s1, len_s2, len(tuple1))
        self.assertEqual(len(tuple2), 1)
        # this will fail
        # self.assertEqual(len(tuple4), 1)
        self.assertEqual(len(tuple3), 2)
        self.assertTrue(type(string1) == str)
        self.assertTrue(type(string2) == str)
        self.assertTrue(string1 == tuple1)
        # should test as type == tuple
        self.assertTrue(type(tuple2) == tuple)
        self.assertTrue(type(tuple4) == tuple)
        self.assertFalse(type(tuple1) == type(tuple2))
        self.assertFalse(type(tuple1) == type(tuple4))
        # this will fail
        # self.assertFalse(len(tuple4) == len(tuple1))
        self.assertFalse(len(tuple2) == len(tuple1))
        self.tupe_as_arg(tuple1, tuple2, tuple3, tuple4)
# stand-alone test execution
if __name__ == '__main__':
    import nose2
    nose2.main(
        argv=[
            'fake',
            '--log-capture',
            'TestChangeMe.default_test',
        ])

您将注意到(几乎)相同的代码调用tuple(string1,)显示为tuple类型,但长度将与字符串长度相同,并且所有成员都是单个字符。

这将导致第137行、第147行、第104行和第115行的断言失败,即使它们看起来与通过的断言相同。

(注意:我在第124行的代码中有一个pudb断点,这是一个很好的调试工具,但是如果愿意,您可以删除它。否则很简单 pip install pudb 使用它。)