Jupyter Notebook，Python3 打印功能：无输出，无错误

Question

Refer to the CODE and OUTPUT below. There is no OUTPUT for the third print statement. An altered print statement in its place such as print(long_word[3:7]) gives output (elin).

# [ ] print the first 4 letters of long_word
# [ ] print the first 4 letters of long_word in reverse
# [ ] print the last 4 letters of long_word in reverse
# [ ] print the letters spanning indexes 3 to 6 of long_word in Reverse
long_word = "timeline"
print(long_word[:4])
print(long_word[3::-1])
print(long_word[3:7:-1])
print(long_word[-1:-5:-1])

OUTPUT

time
emit

enil

What gives? The situation of this question also raised in link below. It is unaddressed as of now.

Answer 1

The slice operation in Python is [start:end:step] , when step=-1 , it represents get values in the reverse direction.

So when use print(long_word[3::-1]) , it is actually from index 3 to index 0 which is determined by reverse direction flag step=-1 . But when use print(long_word[3:7:-1]) , it represents from index 3 to index 7 which is not a reverse order and it is a collision.

Answer 2

If you want to print last four letters in reverse try the below code:

long_word = "Characteristics" 

print(long_word[14:10:-1])     

Result: scit

14 is a starting string index
10 is an ending string index
-1 is used to reverse the string one by one

Answer 3

long_word = "timeline"

print(long_word[0:4])

print(long_word[3::-1])

print(long_word[-1:3:-1])

print(long_word[-3:-7:-1])

This is what I have tried, I think it is an answer of your question.

Answer 4

The correct code is:

long_word = "timeline"
    print(long_word[:4])
    print(long_word[3::-1]) 
    print(long_word[-1:-5:-1])
    print(long_word[6:2:-1])

time
emit
enil
nile

Note that when reversing, you state the wanted ending index first, then the wanted start index - 1 second(except for the 0 index do not subtract one from it), like so:

long_word(wanted ending index: wanted start index - 1: -1)

Answer 5

long_word = "timeline"
print(long_word[:4])
print(long_word[3::-1])
print(long_word[:3:-1])
print(long_word[6:2:-1])