﻿ Python: Check that a string contains only a certain set of characters - w3resource

# Python: Check that a string contains only a certain set of characters

## Python Regular Expression: Exercise-1 with Solution

Write a Python program to check that a string contains only a certain set of characters (in this case a-z, A-Z and 0-9).

Sample Solution:-

Python Code:

``````import re
def is_allowed_specific_char(string):
charRe = re.compile(r'[^a-zA-Z0-9.]')
string = charRe.search(string)
return not bool(string)

print(is_allowed_specific_char("ABCDEFabcdef123450"))
print(is_allowed_specific_char("*&%@#!}{"))
```
```

Sample Output:

```True
False
```

Pictorial Presentation:

Flowchart:

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## Python: Tips of the Day

Getting the last element of a list:

some_list[-1] is the shortest and most Pythonic.

In fact, you can do much more with this syntax. The some_list[-n] syntax gets the nth-to-last element. So some_list[-1] gets the last element, some_list[-2] gets the second to last, etc, all the way down to some_list[-len(some_list)], which gives you the first element.

You can also set list elements in this way. For instance:

```>>> some_list = [1, 2, 3]
>>> some_list[-1] = 5 # Set the last element
>>> some_list[-2] = 3 # Set the second to last element
>>> some_list
[1, 3, 5]
```

Note that getting a list item by index will raise an IndexError if the expected item doesn't exist. This means that some_list[-1] will raise an exception if some_list is empty, because an empty list can't have a last element.

Ref: https://bit.ly/3d8TfFP