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Compare values using JavaScript semantics in Python. Not sure if I got everything right. This is more of a demonstration that JavaScript equality semantics are crazy.
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# Copyright 2021 Mathias Panzenböck | |
# | |
# Permission is hereby granted, free of charge, to any person obtaining a copy | |
# of this software and associated documentation files (the "Software"), to deal | |
# in the Software without restriction, including without limitation the rights | |
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | |
# copies of the Software, and to permit persons to whom the Software is | |
# furnished to do so, subject to the following conditions: | |
# | |
# The above copyright notice and this permission notice shall be included in all | |
# copies or substantial portions of the Software. | |
# | |
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | |
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | |
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | |
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | |
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | |
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE | |
# SOFTWARE. | |
# dict is a stand-in for all plain JavaScript objects in this. | |
def js_equals(a, b) -> bool: | |
if type(a) is type(b): | |
# To be more strict it should be `a is b` if they're list or dict | |
# (i.e. objects in JavaScript). | |
return a == b | |
if isinstance(a, (int, float)): | |
if isinstance(b, (int, float)): | |
return a == b | |
return a == to_float(b) | |
if isinstance(b, (int, float)): | |
return to_float(a) == b | |
if a is None or b is None: | |
return False | |
if isinstance(a, str): | |
if isinstance(b, bool): | |
return to_float(a) == to_float(b) | |
if isinstance(b, (list, dict)): | |
return a == to_string(b) | |
raise TypeError | |
if isinstance(a, bool): | |
return to_float(a) == to_float(b) | |
if isinstance(a, (list, dict)): | |
if isinstance(b, (list, dict)): | |
return False | |
if isinstance(b, str): | |
return to_string(a) == b | |
if isinstance(b, bool): | |
return to_float(a) == to_float(b) | |
raise TypeError | |
raise TypeError | |
def to_float(a) -> float: | |
if a is None: | |
return 0.0 | |
if isinstance(a, list): | |
if not a: | |
return 0.0 | |
elif len(a) > 1: | |
return float('nan') | |
else: | |
return to_float(a[0]) | |
if isinstance(a, dict): | |
return float('nan') | |
try: | |
# XXX: This accepts a little bit too much. I.e. it will allow | |
# 'inf', '+inf', and '-inf', where JavaScript only allows | |
# 'Infinity', '+Infinity', and '-Infinity' (which this | |
# also allows). | |
return float(a) | |
except ValueError: | |
return float('nan') | |
def to_string(a) -> str: | |
if isinstance(a, str): | |
return a | |
if isinstance(a, (int, float)): | |
return str(a) | |
if a is None: | |
return 'null' | |
if a is True: | |
return 'true' | |
if a is False: | |
return 'false' | |
if isinstance(a, list): | |
return ','.join(to_string(b) for b in a) | |
if isinstance(a, dict): | |
return '[object Object]' | |
# Note that this calls a.toString() in JavaScript. | |
# Meaning it returns something different for any object in | |
# JavaScript. E.g. for Date it returns something like: | |
# "Wed Sep 08 2021 05:57:22 GMT+0200 (Central European Summer Time)" | |
# Meanig you can compare a date with a string formated like | |
# that and if the date would be formatting to the string it | |
# yields true. | |
raise TypeError |
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