# Python help with sequences and elements?

• Comp Sci

## Homework Statement

My professor wants us to program on Python, where we have a certain sequence, for example:
sequence = ("one", "two", "three", "four")
I need to replace one of the sequence elements (example: "one") with another element (example: instead of the word "one", I need to put "zero").

2. The attempt at a solution
I really have no idea how to do it, but I guess I have to start with.

sequence = ("one", "two", "three", "four")

Do I need to use something like:

sequence [1 : : 2]

or something else?

Would really appreciate if you guys would help.
I would appreciate even a hint or advice on which path to take to be able to write this.

## Answers and Replies

Related Engineering and Comp Sci Homework Help News on Phys.org
BiGyElLoWhAt
Gold Member
Do you need to replace it everytime it shows up? Might be able to handle this with a simple if statement. Is the sequence a while loop?

I think I figured it out actually! It works when I do it:

sequence = ("one", "two", "three", "four")
sequence2 = ("zero",)+sequence[1::]
print (sequence2)

BiGyElLoWhAt
Gold Member
Cool beans man.

BiGyElLoWhAt
Gold Member
I'm not a huge python guy myself, but I was thinking something like
for(k=0, sequence(k::k)!="one", k++){
print(sequence(k::k)
else print("zero")
}
This looks suspiciously like java though...

BiGyElLoWhAt
Gold Member
lol, i'm not eveen going to change that. :D

lol, i'm not eveen going to change that. :D
Hahah, thank you for trying to help, though. Really appreciate it, man!

Mark44
Mentor

## Homework Statement

My professor wants us to program on Python, where we have a certain sequence, for example:
sequence = ("one", "two", "three", "four")
I need to replace one of the sequence elements (example: "one") with another element (example: instead of the word "one", I need to put "zero").

2. The attempt at a solution
I really have no idea how to do it, but I guess I have to start with.

sequence = ("one", "two", "three", "four")

Do I need to use something like:

sequence [1 : : 2]

or something else?
Something else.
Given the definition you have above, the statement below will change the string at index 1 to the string "four".
Code:
sequence[1] = "four"
Note that indexes start at 0.

Edit: My lack of expertise in Python is showing. Defining a sequence as shown in the Attempt section above makes it a tuple, which is immutable. Defining a sequence as I did, with brackets, makes it a list, and mutable.
acurate said:
Would really appreciate if you guys would help.
I would appreciate even a hint or advice on which path to take to be able to write this.

Last edited:
Dick
Homework Helper
Something else.
Given the definition you have above, the statement below will change the string at index 1 to the string "four".
Code:
sequence[1] = "four"
Note that indexes start at 0.
Well, no it won't. As written 'sequence' is a tuple. Tuples are immutable - you can't change them. To do something like that you'd need to change 'sequence' to a list - which is mutable.

Mark44
Mentor
Well, no it won't. As written 'sequence' is a tuple. Tuples are immutable - you can't change them. To do something like that you'd need to change 'sequence' to a list - which is mutable.
@Dick, it worked for me. This is an exact cut-and-paste from my python session.
Python:
Python 3.4.2 (v3.4.2:ab2c023a9432, Oct  6 2014, 22:15:05) [MSC v.1600 32 bit (Intel)] on win32
>>> sequence = ["one", "two", "three"]
>>> sequence
['one', 'two', 'three']
>>> sequence[1] = "four"
>>> sequence
['one', 'four', 'three']

Dick
Homework Helper
@Dick, it worked for me. This is an exact cut-and-paste from my python session.
Python:
Python 3.4.2 (v3.4.2:ab2c023a9432, Oct  6 2014, 22:15:05) [MSC v.1600 32 bit (Intel)] on win32
>>> sequence = ["one", "two", "three"]
>>> sequence
['one', 'two', 'three']
>>> sequence[1] = "four"
>>> sequence
['one', 'four', 'three']
Sure. That's with 'sequence' a list. Try it with the tuple ('one','two','three').

Mark44
Mentor
You're right, Dick. With parentheses, the sequence is immutable.