Flowchart Iterating through List

Question

Let say I have a list l

l = ['a', 'b', 'c']

To iterate through the list,

for i in l:
    # <some function>

My problem is how should I represet it in a flowchart? Should I use i as index? Thanks in advance.

Asked By: Cheah Ken Win

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Source

Answer 1

Flowcharts are rather miserable for loops

Here is the usual way to do it (from http://etutorials.org/Programming/visual-c-sharp/Part+I+Introducing+Microsoft+Visual+C+.NET/Chapter+5+Flow+of+Control/Building+Loops+Using+Iteration+Statements/)

Flowcharts work best for branching workflows with lots of "ifs"

As you progress, you are getting into smaller and smaller subsets of the overall chart.

They can work for looping, of the type of while do or do while, because these inherently tell you to jump back to a point (or skip over a block).

But for looping controlled by a variable, it’s ugly, I’m afraid.

In your specific case, you could use these terms:

Initialization:

Set index to 0

Conditional expression

Is #index item still within the list? i.e. is index < len(list)?
If false, arrow down to end
If true, continue to "Controlled statement"

Controlled statement

<Some function>

Iteration statement

Increment index
Go back to "Conditional expression"

Answered By: ProfDFrancis

Answer 2

If it’s just in terms of the title, your question is how do you represent it in the flow chart? Whether i is an index,

That’s how you represent the for loop,

In general, you have to have a loop initialization condition, a loop judgment, a loop condition change, and i doesn’t mean index

So for loops might not be very easy to understand in python, because it doesn’t have that, and it might make you wonder why you’re using for directly, and you might even wonder if you’re going through the underlying index,

Then you need to say that python’s for loop causes problems,

python everything is object,

What we call a for loop is actually a foreach loop

Let’s see if we’re using an index,

Let’s do this with a while loop

num_list = [1, 2, 3, 4]

index = 0
while index < len(num_list):
    print(num_list[index])
    index += 1

num_set = {1, 2, 3, 4}

index = 0
while index < len(num_set):
    print(num_set[index])
    index += 1

Traceback (most recent call last):
  File "/home/test.py", line 12, in <module>
    print(num_set[index])
TypeError: 'set' object is not subscriptable

The for loop is aimed at an iterable form

So what you really need to describe is this iterable type, which python implements

Answered By: chrisfang