Python: String beginning or ending match str.startswith (), Str.endswith ()

Problem

You need to check the beginning or end of the string with the specified text pattern, such as the filename suffix, urlscheme, and so on.

Solution Solutions

1. An easy way to check the beginning or end of a string is to use the Str.startswith () or the Str.endswith () method. Like what:

EG1:
>>> filename = ' spam.txt '
Span style= "font-size:12px" >>>> filename.endswith ('. txt ')
True
>>> filename.startswith (' File: ')
false
>>> url = ' http://www.python.org '
>>> url.startswith (' http: ')
True

If you want to check for multiple matches, just put all the matches into a tuple and pass it to StartsWith () or EndsWith () Method:

EG2:
>>> Import OS
>>> filenames = Os.listdir ('. ')
>>> filenames
[' Makefile ', ' foo.c ', ' bar.py ', ' spam.c ', ' spam.h ']
>>> [name for name in filenames if Name.endswith (('. C ', '. h ')]
[' foo.c ', ' spam.c ', ' spam.h '
>>> any (Name.endswith ('. Py ') for name in filenames)
True
>>>

Here is another example:

EG3:
From urllib.request import Urlopen
def read_data (name):
if Name.startswith (' http: ', ' https: ', ' ftp: ')):
return Urlopen (name). Read ()
Else:
With open (name) as F:
return F.read ()
Strangely, you must enter a tuple as a parameter in this method. If you happen to have a list orto ensure that a tuple () is called before the parameter is passed to the tuple type, by selecting the set type. For example:
>>> choices = [' http: ', ' ftp: ']
>>> url = ' http://www.python.org '
>>> Url.startswith (choices)
Traceback (most recent):
File "<stdin>", line 1, in <module>
Typeerror:startswith First arg must be str or a tuple of STR, not list
>>> Url.startswith (tuple (choices))
True
>>>

The startswith () and EndsWith () methods provide a very convenient way to do the beginning of a string andend of the check.

2. Similar operations can also be done using slices, but the code does not look so elegant.

eg
>>> filename = ' spam.txt '
>>> filename[-4:] = = '. txt '
True
>>> url = ' http://www.python.org '
>>> Url[:5] = = ' http: ' or url[:6] = = ' https: ' or url[:4] = = ' ftp: '
True
>>>

3. you can also want to use regular expressions to implement,

eg
>>> Import re
>>> url = ' http://www.python.org '
>>> Re.match (' http:jhttps:jftp: ', url)
<_sre. Sre_match Object at 0x101253098>
>>>
This is a good way to do it, but for a simple match it's a little bit bigger, and the methods in this section are more simple and run faster.

Finally, when combined with other operations such as general data aggregation, StartsWith () and the EndsWith () method is very good. For example, the following statement checks whether a specified file type exists in a folder :
If any (Name.endswith (". C ', '. h ')) for name in Listdir (dirname)):

Python: String beginning or ending match str.startswith (), Str.endswith ()