We Keep Coding

How to assign a new value to the list in running loop

My data cutting loop seems to run ok in the loop, but when it prints the result outside the loop, the contents are unchanged. Presuming it's buggy because I'm trying to assign to what the for loop is running through, but I don't know.
For reference, it's a small web review scraper project I'm working on. To get it formatted to CSV with pandas I think all the data needs to end at the same point (length), so I'm cutting any lists that are longer than the shortest. The values "cust_stars_result, rev_result, cust_res" are all lists with basics strings stored inside, in this case equal to lengths 16, 12, and 15. I try to slice everything down to 12 in the end but the results are overwritten. What is the right/best way to go about this?
star_len = len(cust_stars_result)
rev_len = len(rev_result)
custname_len = len(cust_res)
print('customer name length: ' + str(custname_len) + ' -- review length: ' + str(rev_len) + ' -- star length: ' + str(star_len))
datalen = [star_len, rev_len, custname_len]
print(min(datalen))
datapack = [cust_stars_result, rev_result, cust_res]
# LOOPER FOR CULLING
for data in datapack:
if len(data) != min(datalen):
print("operating culler to make data even length")
print(len(data))
data = data[: min(datalen)]
print(len(data)) #this comes out OK
else:
print("equal length, skipping culler")
pass
print(datapack) # prints the original values

Inside your loop you update the data variable but that's just reassigning the value of that variable. You want to do something like
for i, data in enumerate(datapack):
...
datapack[i] = data[: min(datalen)]
This will update the datapack element

While "trying to assign to what the for loop is running through" is a real issue, in this case the problem is rather that your code is not assigning anything to datapack when you change data. Instead, what it does is assign each item in datapack to data, so when you change data, datapack remain unchanged.
Instead, try either adding each item to new list, and then assigning datapack to equal the new list:
temp = []
for data in datapack:
...
temp.append(data[:min(datalen)])
datapack = temp
Or try using a range or enumerate loop:
for i, data in enumerate(datapack):
...
datapack[i] = data[:min(datalen)]
There are more fancy ways (but less readable and debuggable) to accomplish what you're doing here (slicing off the end of the list), such as the below which uses list comprehension and map:
mindatalen = min(map(len, datapack))
datapack = [data[:mindatalen]for data in datapack]

search for the lowest priced item function

I'm adding a function to a class to output the item with the lowest price but what I'm getting are all the prices. See photo and code. What am I missing on the code?
def get_low_price(self):
self.get_total_toys()
#To check if toybox is empty or not
if self.total > 0:
msg = f'The toy box contains {self.total} toys\n'
for a_toy in self.all_toys:
self.get_total_cost()
msg += f'A {(a_toy.colour).lower()} {a_toy.name} which cost ${a_toy.price:.2f}\n'
for i in [a_toy.price]:
i = ([i])
print(min(i))
return f'{msg}Total cost: ${self.cost_total:.2f}'

This inner loop isn't doing anything useful:
for i in [a_toy.price]:
i = ([i])
print(min(i))
Here a_toy is already just a single toy. Looping over a new list containing only its price doesn't accomplish anything you could get just by accessing a_toy.price directly, and rebinding the loop variable i to another new list (in extraneous parentheses) doesn't add anything.
I think you want to move all of the min-finding logic outside of the earlier loop, unless you want to compare prices yourself. Instead, you can use just one min call, outside of the loop:
for a_toy in self.all_toys: # don't include the stuff below in this loop
...
cheapest = min(self.all_toys, key=lambda t: t.price) # find cheapest
# do something down here with cheapest, or cheapest.name, maybe

I didn't understand what exactly you are trying to do using the for loop in that method. If you are thinking that i = ([i]) is going to append price to a list then it's wrong. Use the below logic and rewrite your method. It will work.
toys = {"doll": 5, "hulk": 10, "teddy": 15}
cheapest_toy_name = ""
cheapest_toy_price = float("inf")
for k, v in toys.items():
if cheapest_toy_price > v:
cheapest_toy_price = v
cheapest_toy_name = k
print(cheapest_toy_name)

How to create a dataframe with a dynamic text parameter passed to a function in Python

(I'm pretty new to Python,(and even to coding)forgive me for my stupidity.)
I'm trying to pass a text value and a list as parameters to a function. Here's an example :
Names = File['Student_Name']
Scores = File['Marks']
for a in range(0,100):
Student_Name = [Names[a]]
Marks = []
NewDf = pd.DataFrame(PreCovid(Student_Name,Marks))
Master_Sheet_PreCovid = NewDf
Master_Sheet_PreCovid
What I wish to achieve is passing Name of a Student, as a string, one at a time, to the function. In this code, I'm vaguely creating a df with each loop iteration, which obviously will only return me the last value, however, I wish to get the output for complete list of Students. What modifications/additions do I make in this code to make it work.
I followed this thread, Why the function is only returning the last value? , which was similar to my query, however might not work with my requirements.
Edited : I actually have 2 sheets that I'm fetching my data from,one is a Main Sheet,that has all the data with redundancy,I've a Rule book with unique values and the rules for calculation.In this code I'm only fetching values from Rule Book,then going to the function,fetching data based on these values from Main Sheet,performing my calculations,creating a new dataframe,inserting the values I get here into that dataframe as well,and return the Final dataframe.Right now, the calculation tested based only on Student_Name has worked, but now I've a bigger problem of calculating also based on Marks.
At the risk of sounding arrogant, I only wish to pass the name as string, not as list.
Again, I'm sorry about the stupidity of my query.

Give it a try:
Names = File['Student_Name']
Scores = File['Marks']
Master_Sheet_PreCovid = []
for a in range(0,100):
Student_Name = [Names[a]]
Marks = []
NewDf = pd.DataFrame(PreCovid(Student_Name,Marks))
Master_Sheet_PreCovid.append(NewDf)
Master_Sheet_PreCovid = pd.concat(Master_Sheet_PreCovid)
print(Master_Sheet_PreCovid)

do variables need to be instantiated before while loop python

i'm trying to scrape more 500 posts with the reddit api - without praw. however, since i'm only allowed 100 posts at a time, i'm saving the scraped objects in an array called subreddit_content and will be scraping until there are 500 posts in subreddit_content.
the code below gives me NameError: name 'subreddit_content_more' is not defined. if i instantiate subreddit_data_more = None before the while loop, i get TypeError: 'NoneType' object is not subscriptable. i've tried the same thing with a for loop but get the same results.
EDIT: updated code, while loop now uses subreddit_data instead of subreddit_data_more, but now getting TypeError: 'Response' object is not subscriptable despite converting subreddit_data to json.
subreddit_data = requests.get(f'https://api.reddit.com/r/{subreddit}/hot?limit=100', headers={'User-Agent': 'windows:requests (by /u/xxx)'})
subreddit_content = subreddit_data.json()['data']['children']
lastline_json = subreddit_content[-1]['data']['name']
while (len(subreddit_content) < 500):
subreddit_data = requests.get(f'https://api.reddit.com/r/{subreddit}/hot?limit=100&after={lastline_json}', headers={'User-Agent': 'windows:requests (by /u/xxx)'})
subreddit_content = subreddit_content.append(subreddit_data.json()['data']['children'])
lastline_json = subreddit_data[-1]['data']['name']
time.sleep(2.5)
EDIT2: using .extend instead of .append and removing the variable assignment in the loop seemed to do the trick. this is the snippet of working code (also renamed my variables for readability, courtesy of Wups):
data = requests.get(f'https://api.reddit.com/r/{subreddit}/hot?limit=100', headers={'User-Agent': 'windows:requests (by /u/xxx)'})
content_list = data.json()['data']['children']
lastline_name = content_list[-1]['data']['name']
while (len(content_list) < 500):
data = requests.get(f'https://api.reddit.com/r/{subreddit}/hot?limit=100&after={lastline_name}', headers={'User-Agent': 'windows:requests (by /u/xxx)'})
content_list.extend(data.json()['data']['children'])
lastline_name = content_list[-1]['data']['name']
time.sleep(2)

You want to just add one list to another list, but you're doing it wrong. One way to do that is:
the_next_hundred_records = subreddit_data.json()['data']['children']
subreddit_content.extend(the_next_hundred_records)
compare append and extend at https://docs.python.org/3/tutorial/datastructures.html
What you did with append was add the full list of the next 100 as a single sub-list at position 101. Then, because list.append returns None, you set subreddit_content = None
Let's try some smaller numbers so you can see what's going on in the debugger. Here is your code, super simplified, except instead of doing requests to get a list from subreddit, I just made a small list. Same thing, really. And I used multiples of ten instead of 100.
def do_query(start):
return list(range(start, start+10))
# content is initialized to a list by the first query
content = do_query(0)
while len(content) < 50:
next_number = len(content)
# there are a few valid ways to add to a list. Here's one.
content.extend(do_query(next_number))
for x in content:
print(x)
It would be better to use a generator, but maybe that's a later topic. Also, you might have problems if the subreddit actually has less than 500 records.

how we can use variables, which are described inside the loop, out side the loop in python

Below is my code. Here, I am trying to read the variable gobs(x) from an input file and then I want to use it for other calculations, eg., computing error(x). But, I found, I can read it from input file properly within the loop, but when trying to use it outside the loop, only the first data is getting transferred. For all 100 data, which I read as gobs(x) inside the loop, it is showing the value of last data only, when I am using it outside the loop.
code started below
constant = 99
x0=50
z0=5
def gsyn (x):
return (constant*z0)/(z0**2+(x-x0)**2)
with open ('Grav_H_Cyln_v3_output.txt') as finp:
lines=finp.readlines()
for line in lines:
g=float(line)
x=line
def gobs (x):
return g
print (gobs(x)) # here, gobs(x) is printing properly
def error(x):
return (gsyn(x)-gobs(x))
for i in range (1, 100, 1):
x=i
print (error(x)) # here, only the first value of gobs(x) is coming
print ('stop')

This seems like a very odd solution to what is fundamentally a very simple problem. Make gobs a dictionary so you can set or retrieve gobs[x] at will.
gobs = dict()
with open ('Grav_H_Cyln_v3_output.txt') as finp:
lines=finp.readlines()
for line in lines:
g=float(line)
gobs[line] = g
print (gobs[line])

You could try creating a vector gobs[] outside the loop, and filling it up within the loop over lines.
That should do.

Instead of reassigning the value of x on each iteration of your loop, append i to a list that is declared outside of the if-block scope.
x = []
for i in range (1, 100, 1):
x.append(i)
print(x)