Linked Questions
1,660 questions linked to/from How slicing in Python works
2721 votes
16 answers
4.1m views
How do I get a substring of a string in Python? [duplicate]
I want to get a new string from the third character to the end of the string, e.g. myString[2:end]. If omitting the second part means 'to the end', and if you omit the first part, does it start from ...
93 votes
7 answers
23k views
Why does Python start at index -1 (as opposed to 0) when indexing a list from the end? [duplicate]
list = ["a", "b", "c", "d"] print(list[3]) # Number 3 is "d" print(list[-4]) # Number -4 is "a"
187 votes
7 answers
1.1m views
How to overcome TypeError: unhashable type: 'list' [duplicate]
I'm trying to take a file that looks like this: AAA x 111 AAB x 111 AAA x 112 AAC x 123 ... And use a dictionary so that the output looks like this {AAA: ['111', '112'], AAB: ['111'], AAC: [123], ...}...
176 votes
3 answers
382k views
Colon (:) in Python list index [duplicate]
I'm new to Python. I see : used in list indices especially when it's associated with function calls. Python 2.7 documentation suggests that lists.append translates to a[len(a):] = [x]. Why does one ...
107 votes
2 answers
364k views
What is the meaning of "int(a[::-1])" in Python? [duplicate]
I cannot understand this. I have seen this in people's code. But cannot figure out what it does. This is in Python. str(int(a[::-1]))
111 votes
2 answers
200k views
How to get everything from the list except the first element using list slicing [duplicate]
I want to parse something like: list = ['A', 'B', 'C'] And using list slicing have it return to me everything but the first index: ['B', 'C'] I tried list[:-1], list[::-1], list[0:-1], etc. What I ...
61 votes
4 answers
249k views
What does [:-1] mean/do in python? [duplicate]
Working on a python assignment and was curious as to what [:-1] means in the context of the following code: instructions = f.readline()[:-1] Have searched on here on S.O. and on Google but to no ...
32 votes
9 answers
80k views
I don't understand slicing with negative bounds in Python. How is this supposed to work? [duplicate]
I am a newbie to Python and have come across the following example in my book that is not explained very well. Here is my print out from the interpreter: >>> s = 'spam' >>> s[:-1] '...
37 votes
6 answers
121k views
What does list[x::y] do? [duplicate]
Possible Duplicate: Good Primer for Python Slice Notation I've been reading over some sample code lately and I've read quite a few websites but I just can't seem to get the query right to give me ...
33 votes
5 answers
163k views
What does :-1 mean in python? [duplicate]
I'm trying to port some Python code to C, but I came across this line and I can't figure out what it means: if message.startswith('<stream:stream'): message = message[:-1] + ' />' I ...
23 votes
6 answers
136k views
Python: What does for x in A[1:] mean? [duplicate]
I was trying to understand Kadane's algorithm from Wikipedia, when I found this: def max_subarray(A): max_ending_here = max_so_far = A[0] for x in A[1:]: max_ending_here = max(x, ...
41 votes
1 answer
198k views
What is the meaning of [:] in python [duplicate]
What does the line del taglist[:] do in the code below? import urllib from bs4 import BeautifulSoup taglist=list() url=raw_input("Enter URL: ") count=int(raw_input("Enter count:")) position=int(...
20 votes
1 answer
68k views
plt.plot meaning of [:,0] and [:,1] [duplicate]
I am plotting a graph using plt.plot using information found online. However, I do not know what the y[:,0] means: plt.plot(t, y[:,0], label= 'active Mos') Similarly, I see y[:,1] a lot too... ...
15 votes
3 answers
149k views
Extracting a range of data from a python list [duplicate]
I have a list of unicode values. To the best of my knowledge I can use list[starting location:length to select] to select a range of values from a list, right? I have a list of 78 unicode values, ...
29 votes
2 answers
21k views
What does extended slice syntax actually do for negative steps? [duplicate]
The extended slice syntax in python has been explained to me as "a[n:m:k] returns every kth element from n to m". This gives me a good idea what to expect when k is positive. But I'm lost on how to ...