关于示例代码括号内容及Python字符串切片[4::2]的技术咨询

Hey there! Let's break this down step by step so it clicks perfectly.

First, let's clarify what the string s actually is after concatenation:

s = 'We\'re' + 'Here'

This combines the two strings into "We'reHere". Let's map out each character with its index (remember, Python uses 0-based indexing for strings):

Next, let's unpack the slicing syntax s[4::2]. Python string slicing follows the pattern:

string[start:end:step]

Here's what each part means:

• start: The index where we begin extracting characters (inclusive). In your case, this is 4.
• end: The index where we stop extracting (exclusive). When you leave this blank, it defaults to the end of the string.
• step: The number of positions to skip between each character we extract. A positive step means we move left-to-right; a negative step would reverse direction. Your step is 2.

Applying this to your example:

1. Start at index 4: we take the character e.
2. Skip 2 positions (4 + 2 = 6): take the character e at index 6.
3. Skip another 2 positions (6 + 2 = 8): take the character e at index 8.
4. Next, we'd skip to 10, which is beyond the length of the string (our string only goes up to index 8), so we stop.

Putting those characters together gives you eee—exactly the output you saw!

To recap: when you use [4::2], you're saying "start at index 4, keep grabbing every 2nd character until the end of the string."

内容的提问来源于stack exchange，提问作者theyoungcoder