Python 3：如何检查字符串是否可以是有效变量？

Question

我有一个字符串，想检查它是否可以用作有效变量而不会出现语法错误。 例如

def variableName(string):
    #if string is valid variable name:
        #return True
    #else:
        #return False

input >>> variableName("validVariable")
output >>> True
input >>> variableName("992variable")
output >>> False

我不想使用.isidentifier（）。 我想发挥自己的作用。

Answer 1

以下答案仅适用于“旧式” Python-2.7标识符；

"validVariable".isidentifier()
#True
"992variable".isidentifier()
#False

由于您在我发布答案后更改了问题，因此请考虑编写正则表达式：

re.match(r"[_a-z]\w*$", yourstring,flags=re.I)

Answer 2

在Python 3中，有效的标识符可以包含ASCII范围之外的字符，因为您不想使用str.isidentifier ，可以在Python中编写自己的版本。

它的规范可以在这里找到： https : //www.python.org/dev/peps/pep-3131/#specification-of-language-changes

实现方式：

import keyword
import re
import unicodedata


def is_other_id_start(char):
    """
    Item belongs to Other_ID_Start in
    http://unicode.org/Public/UNIDATA/PropList.txt
    """
    return bool(re.match(r'[\u1885-\u1886\u2118\u212E\u309B-\u309C]', char))


def is_other_id_continue(char):
    """
    Item belongs to Other_ID_Continue in
    http://unicode.org/Public/UNIDATA/PropList.txt
    """
    return bool(re.match(r'[\u00B7\u0387\u1369-\u1371\u19DA]', char))


def is_xid_start(char):

    # ID_Start is defined as all characters having one of
    # the general categories uppercase letters(Lu), lowercase
    # letters(Ll), titlecase letters(Lt), modifier letters(Lm),
    # other letters(Lo), letter numbers(Nl), the underscore, and
    # characters carrying the Other_ID_Start property. XID_Start
    # then closes this set under normalization, by removing all
    # characters whose NFKC normalization is not of the form
    # ID_Start ID_Continue * anymore.

    category = unicodedata.category(char)
    return (
        category in {'Lu', 'Ll', 'Lt', 'Lm', 'Lo', 'Nl'} or
        is_other_id_start(char)
    )


def is_xid_continue(char):
    # ID_Continue is defined as all characters in ID_Start, plus
    # nonspacing marks (Mn), spacing combining marks (Mc), decimal
    # number (Nd), connector punctuations (Pc), and characters
    # carryig the Other_ID_Continue property. Again, XID_Continue
    # closes this set under NFKC-normalization; it also adds U+00B7
    # to support Catalan.

    category = unicodedata.category(char)
    return (
        is_xid_start(char) or
        category in {'Mn', 'Mc', 'Nd', 'Pc'} or
        is_other_id_continue(char)
    )


def is_valid_identifier(name):
    # All identifiers are converted into the normal form NFKC
    # while parsing; comparison of identifiers is based on NFKC.
    name = unicodedata.normalize(
        'NFKC', name
    )

    # check if it's a keyword
    if keyword.iskeyword(name):
        return False

    # The identifier syntax is <XID_Start> <XID_Continue>*.
    if not (is_xid_start(name[0]) or name[0] == '_'):
        return False

    return all(is_xid_continue(char) for char in name[1:])

if __name__ == '__main__':
    # From goo.gl/pvpYg6
    assert is_valid_identifier("a") is True
    assert is_valid_identifier("Z") is True
    assert is_valid_identifier("_") is True
    assert is_valid_identifier("b0") is True
    assert is_valid_identifier("bc") is True
    assert is_valid_identifier("b_") is True
    assert is_valid_identifier("µ") is True
    assert is_valid_identifier("𝔘𝔫𝔦𝔠𝔬𝔡𝔢") is True

    assert is_valid_identifier(" ") is False
    assert is_valid_identifier("[") is False
    assert is_valid_identifier("©") is False
    assert is_valid_identifier("0") is False

---

您可以在此处和此处分别检查CPython和Pypy的实现。

Answer 3

您可以使用正则表达式。

例如：

isValidIdentifier = re.match("[A-Za-z_](0-9A-Za-z_)*",identifier)

请注意，他只检查字母数字字符。 实际标准支持其他字符。 看到这里： https : //www.python.org/dev/peps/pep-3131/

您可能还需要排除诸如def，True，False等保留字...请参见此处： https ： //www.programiz.com/python-programming/keywords-identifier