String Boolean Methods in Python

Today we’ll be talking about string boolean methods.

In my previous articles I covered quite a few string methods. If you haven’t read those articles, feel free to do it. Here they are:

1) formatting methods

2) statistical methods

3) searching methods

The startswith and endswith Methods

There are a couple of methods that return True or False. One of them is startswith(prefix[, start, past]), which checks if the string or substring (if the optional start and past parameters are given) start with prefix:

>>> text = "So, come and help me."
>>> text.startswith("So")
True

Let’s check the substring from index 4 to the end:

>>> text.startswith("c", 4)
True

Now let’s check the slice between index 3 and 7:

>>> text.startswith("So", 3, 8)
False

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There’s also the method endswith(suffix[, start, past]), which checks if the string or substring (if the optional start and past parameters are given) ends with suffix:

>>> text = "Are you OK?"

So, does the string end with a question mark? Yes, it does.

>>> print(text.endswith("?"))
True

Does the slice between index 1 and 6 (so “re you”) end in “ou”. Yep.

>>> print(text.endswith("ou", 1, 7))
True

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The islower, isupper and istitle Boolean Methods

The method islower returns True if the all the letters in the string are lowercase:

>>> "we are all lowercase letters! more than 10 of us.".islower()
True

The isupper method returns True if all the letters in the string are uppercase:

>>> "10 GREEN BOTTLES COMIN' TO TOWN".isupper()
True

The method istitle returns True if all the letters in the string are titlecase characters, i.e. each word starts with a capital letter. Other characters are ignored, but there must be at least one letter.

>>> "The War Of The Giants".istitle()
True

>>> "The War of the Giants".istitle()
False

>>> "5 Orange Bathtubs".istitle()
True

>>> "$5 Journey - The Beginning".istitle()
True

>>> "14".istitle()
False

>>> "A14".istitle()
True

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Here’s the video version of the article: