You’d like to get a subset of a string or array with a single expression. For example, you have the following variables storing some data that you need to manipulate:
hello_world_string = "Hello World!" num_string = "012345"
Since in Python, strings are arrays, we can use the same syntax for both object types.
Slicing segments an array and returns that segment.
In the example below, a string is segmented to return a single word from within the string:
hello_world_string = "Hello World!" world = hello_world_string[7:12] print(world)
Output:
World
Slicing requires a start and a stop:
array[start:stop]
The start is the index of the array that you would like the slice to begin with, the stop is the index of the array you would like to stop at.
The value of the array at the stop index is not included in the slice.
num_string = "012345" zero_to_four = num_string[0:5] print(zero_to_four)
Output:
01234
If an index is not provided for start, the slice will begin at the start of the array.
If an index is not provided for stop, the slice will end after the end of the array.
# Returns entire array array[:]
For example:
num_string = "012345" zero_to_five = num_string[:] print(zero_to_five)
Output:
012345
Slicing can also use a third value called step:
array[start:stop:step]
The step designates the manner in which the slice can walk through the array.
Assigning a step of 2
will include values from the array every two “steps”.
In the example below, a string is sliced starting at index 2, stopping when the array is complete, and taking the values at every second step.
num_string = "0123456" even_nums = num_string[2::2] print(even_nums)
Output:
246
Slicing can use negative indexing. With negative indexing, the last value in an array is -1, the second last is -2, and so on.
For example:
num_string = "012345" one_two_three = num_string[-5:-2] print(one_two_three)
Output:
123
Use negative indexing to step through an array in reverse.
For example:
num_string = "012345" reverse_string = num_string[::-1] print(reverse_string)
Output:
543210
Get actionable, code-level insights to resolve Python performance bottlenecks and errors.
Create a free Sentry account
Create a Python project and note your DSN
Grab the Sentry Python SDK
pip install --upgrade sentry-sdk
import sentry_sdk sentry_sdk.init( "https://<key>@sentry.io/<project>", # Set traces_sample_rate to 1.0 to capture 100% # of transactions for performance monitoring. # We recommend adjusting this value in production. traces_sample_rate=1.0, )
Loved by over 4 million developers and more than 90,000 organizations worldwide, Sentry provides code-level observability to many of the world’s best-known companies like Disney, Peloton, Cloudflare, Eventbrite, Slack, Supercell, and Rockstar Games. Each month we process billions of exceptions from the most popular products on the internet.