Python's not that close to English

Zecc

I've just substituted fifty-ish instances of this pattern.

if params["required_param"] is u"" or None:
    # Complain about user error
else:
    # Assume params["required_param"] is a non-empty string

I've also found this pattern twice:

if string_or_none is not (u"" or None):
    # Assume string_or_none is a non-empty string

Fortunately, we've never had a value of None reach the first test or u"" reach the second.

Notes for those not acquainted to Python:

"is not" is its own operator, such that "x is not y" means "not (x is y)" rather than "x is (not y)";
"or" has lower precedence than "is not"
"x or y" evaluates to y if x is falsy.

accalia

@Zecc said:

if string_or_none is not (u"" or None):

if string_or_none not in [u"", None]:

FTFY

TwelveBaud

import clr;
import System;

if System.String.IsNullOrEmpty(params["required_param"]):
    # Suggest user inadvertence
else:
    # Assume params["required_param"] is a non-empty string

Zecc

@accalia said:

```
if string_or_none not in [u"", None]:
FTFY</blockquote>

I went with a simple:

 if string_or_none:

Also, @discoursebot.

discoursebot

@Zecc - Days Since Last Discourse Bug: -1

accalia

ok, yes that would work, but it would also catch the case where string_or_null is the number 0, or the boolean value False, or even any class instance that bool(string_or_null) returns False for.

not sure if that is desired or not, but my change preserves original intent.

:-P

Zecc

And if you're that interested, the first if I rewrote as:

if not params.get("required_param"):

get() returns the value in the dictionary if the key is present or a default if it's not, where the default default is None if no default is given.

Zecc

@accalia said:

ok, yes that would work, but it would also catch the case where string_or_null is the number 0, or the boolean value False, or even any class instance that bool(string_or_null) returns False for.

not sure if that is desired or not, but my change preserves original intent.

That's true.

Zecc

You've made me check.

>>> "" is u""
False
>>> "" == u""
True
>>> "" in [u""]
True

Zecc

It just occurred to me that these strings aren't being trimmed or checked for something other than whitespace.

sigh

Yamikuronue

@Zecc said:

get() returns the value in the dictionary if the key is present or a default if it's not

I dunno python, but there's a common error here in JS land if the value itself is falsey...

anonymous234

Of course, if you were using this string for something like opening a file, the pythonest way would be:

try:
    #stuff
except ValueError:
    #complain to user