Python string method find() and membership operation (in,not in)?

Question

In core python programming,2nd edition.

6.3 Strings and Operators.

"The membership question asks whether a (sub)string appears in a (nother) string. true is returned if that character appears in the string and False otherwise. Note that the membership operation is not used to determine if a substring is within a string. Such functionality can be accomplished by using the string methods or string module functions find() or index() (and their brethren rfind() and rindex()). "

I'm confused by this.So what dose it mean by saying"Note that the membership operation is not used to determine if a substring is within a string." Shouldn't i use in or not in to find out whether a substring is within a string?

That has to be a typo. The only way that sentence makes sense is if it's supposed to be: "Note that the membership operation is not used to determine where a substring is within a string." since index and find return a location instead of just true/false. — tzaman
– tzaman, Commented Oct 30, 2015 at 3:06

Ignacio Vazquez-Abrams · Accepted Answer · 2015-10-30 03:05:41Z

2

You are correct. Membership/containment can be used to detect presence of a substring within a string. Using it for a single character is simply a degenerate form of substring searching, since a "single character" in Python is a string of length 1.

>>> 'foo' in 'foobar'
True
>>> 'fba' in 'foobar'
False

answered Oct 30, 2015 at 3:05

Ignacio Vazquez-Abrams

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2 Comments

Kethylar Over a year ago

Thank you all for answering my question, how do you think about @tzaman's comment, he point out that this maybe a typo.

Ignacio Vazquez-Abrams Over a year ago

@Kethylar: Correcting that would make the sentence make sense. The previous two sentences also need to be changed, since the first talks about a substring and the second switches to a character.

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