但是在删除的值之后,值的重复上移使得这种技术对于长列表来说效率很低。这段代码的可视化执行在autbor.com/iteratebackwards1进行。你可以在图 8-3 中看到向前迭代和向后迭代的区别。 图8-3:向前(左)和向后(右)迭代时从列表中删除偶数 类似地,当您向后遍历列表时,您可以将项目添加到列表的末尾。在交互式 S
但是在删除的值之后,值的重复上移使得这种技术对于长列表来说效率很低。这段代码的可视化执行在autbor.com/iteratebackwards1进行。你可以在图 8-3 中看到向前迭代和向后迭代的区别。 图8-3:向前(左)和向后(右)迭代时从列表中删除偶数 类似地,当您向后遍历列表时,您可以将项目添加到列表的末尾。在交互式 Sh...
>>> sys.getsizeof('a much longer string than just "cat"') 85 (在我使用的 Python 版本中,string 对象的开销占用 49 个字节,而字符串中的每个实际字符占用 1 个字节。)但是包含这些字符串中任何一个的列表都要占用 72 个字节,不管字符串有多长: >>> sys.getsizeof(['cat']) 72 >>> sys.gets...
The reason why this loop works is because Python considers a “string” as a sequence of characters instead of looking at the string as a whole. Using the for loop to iterate over a Python list or tuple ListsandTuplesare iterable objects. Let’s look at how we can loop over the elemen...
# The 3rd argument of range means we iterate backwards, reducing the count # of i by 1 for i in range(n, -1, -1): heapify(nums, n, i) # Move the root of the max heap to the end of for i in range(n - 1, 0, -1): nums[i], nums[0] = nums[0], nums[i] heapify(...
Just like before, you can use sorted() to iterate through each element of the iterable you pass in. In a string, each element means each character, including spaces. Note: Python sorts strings lexicographically by comparing Unicode code points of the individual characters from left to right. ...
for i in range(5) is a loop that iterates over the numbers from 0 to 4, inclusive. The range parameters start, stop, and step define where the sequence begins, ends, and the interval between numbers. Ranges can go backward in Python by using a negative step value and reversed by usin...
# assign the integer 1 to the variable i (also "creates" the variable") i = 1 # assign the string "foobar" to the variable s s = "foobar" # Add 5 to the integer i - this is equivalent to i = i + 5 i += 5 # i now holds the integer 6. # Try to add i and s - th...
The ordering is the important item to understand to get list comprehensions right. It is like a loop written backwards. To illustrate this, the following two examples produce the same result, one with a loop and the other one with a list comprehension:...
这段代码的可视化执行在autbor.com/iteratebackwards2进行。通过向后迭代,我们可以在列表中添加或删除条目。但是这可能很难做到正确,因为对这一基本技术的微小改变最终可能会引入错误。创建新列表比修改原始列表简单得多。正如 Python 核心开发者 Raymond Hettinger 所说: ...