Question

What will the following code display? mystring = 'abcdefg' print(mystring[:3])

Short answer

```python mystring = 'abcdefg' print(mystring[:3]) ``` Answer: The output will be 'abc'.

Step-by-step solution

Understand the given code snippet

In this code snippet, a string named 'mystring' is assigned the value 'abcdefg'. Then, a part of the string is printed using slicing with the notation 'mystring[:3]'.

Explain String Slicing

In Python, string slicing means extracting a portion of a given string. This can be done using indexing. To extract a part of a string, you can use the format 'string[start:end]' where 'start' is the index of the first character you want to include, and 'end' is the index of the first character you want to exclude. For instance, if you have a string 'abcdefg' and wanted to extract the first three characters, you would use 'string[0:3]'. It is essential to remember that string indexing starts from 0 in Python.

Analyze the Print Statement

In this code snippet, the print statement is 'print(mystring[:3])'. Here, the start index is not specified, which by default means that it starts from the index 0. The end index is 3, indicating that the extracted substring should end before the third index element. The slicing operation will include the characters from index 0 to 2.

Determine the Output

Given the slicing operation, the output will be a substring that includes characters from the index 0 to 2, which are 'a', 'b', and 'c'. Therefore, the final output displayed will be 'abc'.

Key concepts

Python String Manipulation

Manipulating strings in Python is a fundamental skill that enables programmers to perform a variety of operations on text data. Python strings are immutable, meaning once you create a string, you cannot change its content. However, you can perform actions to create new strings based on the original, such as concatenation, transformation, and, as highlighted in our exercise, slicing.

Understanding how to work with strings is crucial for tasks like data parsing, file manipulation, and most types of text processing. Common string manipulations include changing case, trimming whitespace, replacing substrings, and splitting strings into lists. Each character within a string can be accessed using an index and strings can be concatenated to form larger strings. These abilities add versatility to string manipulation in Python.

String Indexing

String indexing in Python is the way to access specific characters in a string. Python strings are zero-indexed, meaning the first character is at index 0, the second at index 1, and so on. For example, in the string 'Python', the character 'P' is at index 0, and 'n' is at index 5.

You can also use negative indexing to start counting from the end of the string instead. In this case, 'n' would be at index -1, 'o' at index -2, and so forth. Understanding indexing is key to extracting substrings; it allows you to pinpoint exactly where to start and stop the slice. Besides individual character access, string indexing allows for slicing, which takes a range of characters from the string.

Substring Extraction

Substring extraction is about retrieving a portion of a string using slicing. In Python, this is achieved using the syntax 'string[start:stop:step]', where 'start' is the index to begin the slice, 'stop' is the index to end it, and 'step' allows skipping characters within the slice.

For example, 'string[1:5]' will extract the substring from index 1 up to, but not including, index 5. If you omit the 'start', like 'string[:5]', Python starts from the beginning of the string. Similarly, omitting the 'stop' index, as in 'string[2:]', Python will extract up to the end of the string. When 'step' is used, such as 'string[1:5:2]', it will take every second character from index 1 to 4. The 'step' can also be negative, which causes the slice to be taken from right to left, effectively reversing the string if 'start' and 'stop' are omitted.