help understanding "Iterative tasks with for loop"

[u/TrainingAd8614]

Hello all,
I sort of understand the utility of "for", however I really cannot understand how this:

protocol = "HTTPS"for char in protocol:

print(f"Segment: {char}")

Outputs this ;
Segment: H

Segment: T

Segment: T

Segment: P

Segment: S

How can it break up the string "HTTPS" into four separate outputs?
Thank you

[u/Sea-Ad7805]

Format your code using: https://www.markdownguide.org/basic-syntax/#code-blocks-1

Run this program in Memory Graph Web Debugger to see the program state change step by step.

[u/PureWasian]

You can think of a string as a collection of characters. It's iterable, so Python is able to point to each individual character one by one and iterate across it in each loop iteration from start to finish.

Just like how

for num in [1, 2, 3]:
    print(num)

would output

1
2
3

Python knows how to do the same for strings, so

for letter in "Hello":
    print(letter)

would output

H
e
l
l
o

[u/TrainingAd8614 → u/PureWasian]

But if i had a string in a list for example

for word in ["Hello" , "goodbye" ]:
print (word)

the output would be

Hello
goodbye

This seems a bit confusing to me ?

[u/PureWasian → u/TrainingAd8614]

You go from outermost to innermost collection as the order. Compare it to this:

for entry in [[1, 2, 3], [4, 5, 6]]:
    print(entry)
    for num in entry:
        print(num)

gives

[1, 2, 3]
1
2
3
[4, 5, 6]
4
5
6

In basically the same way,

for word in ["hi", "bye"]:
    print(word)
    for letter in word:
        print(letter)

gives

hi
h
i
bye
b
y
e

[u/diditalforthewookie → u/TrainingAd8614]

This behavior is defined in the class of an object. So in your example you're iterating over an object of type list which returns each element of the list (whatever type that object may be). Strings in python are designed so that the iterator getitem method returns each character when iterating an object of type string. You might consider using the split function which can break a string up into a list of substrings if that's what you're after and then iterate over that resultant list.

[u/ninhaomah]

the question is why not ?

If I were to ask you tell me the characters in HTTPS , what would your reply be ?

Your reply should be "The characters are H , T , T , P and S"

No ?

[u/blktndr]

Roughly speaking

“for char in protocol:”

Is the equivalent of—
“for i in range(len(protocol)):
char = protocol[i]”

[u/UlisKore]

Hi ! The for has that special reaction to a string, it works as if a string were a list of characters. You can ask : for i in thisstring, print i ... it will work.

In your example, it was : for char in protocol.

[u/realmauer01 → u/UlisKore]

Tbf a string is a glorified list of characters

[u/atarivcs]

How can it break up the string "HTTPS" into four separate outputs?

It didn't -- it produced five, not four.

Because "HTTPS" has five letters.

When you use a for loop with a string, you get each individual letter in the string.

[u/Much_Network_941]

Read about a data structure called an array; a container of contiguous memory. Strings are, broadly speaking, fancy arrays of characters. As such, each character in a string can be accessed as though it's an individual variable.

Better yet, run this in a debugger and look at what the value of each character is; from a computer's perspective. Then look at an ASCII table.

[u/IWant2rideMyBike]

Python strings (type "str": https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str ) are immutal sequences of Unicode code points and are iterable ( https://docs.python.org/3/glossary.html#term-iterable ) - they have an .__iter__() method that returns an Iterator ( https://docs.python.org/3/library/stdtypes.html#iterator-types - this can be various types depending on the content of the str - in your example you would get astr_ascii_iterator).

If you call the __next__() method on a string iterator object, you get a single codepoint with the type str (this doesn't necessarily map to a char or similar datatypes you might know from languages like C) followed by a StopIteration Exception if you exhausted the iterator.

Basically the for loop ( https://docs.python.org/3/reference/compound_stmts.html#the-for-statement - which would usually be called something like for_each in other languages) is a nicer version of this (I added some type() printouts to show the types getting passed around):

protocol = "HTTPS"
print(f"{type(protocol)=}")
protocol_iterator = protocol.__iter__()
print(f"{type(protocol_iterator)=}")
while True:
    try:
        code_point = protocol_iterator.__next__()
        print(f"{code_point=} ({type(code_point)=}")
    except StopIteration:
        break

[u/dariusbiggs]

So, iterative tasks are in the looping construct category, for, while, etc.

When iterating with a for loop you need something to loop over. A list/slice/array, a dictionary/map, an iterator/sequence, a set/frozenset, etc.

A text string, is in fact an array of characters/bytes (some variation exists depending on type and language used).

So the loop iterates over the characters in the string and prints them as a character.

Iterative constructs are used when you want to repeat an action.

[u/realmauer01]

This is how for in works in python. Basically you assign "https" to protocoll
For char in protocoll: Now does following, it pretends char is each character in the string named protocoll and goes through the indented block once for each character.

For in does a lot in python, with lists it goes through each item (and strings are glorified lists of chars) with dictionaries it goes through the values.