Develop Reference

Can someone explain why var = input() in python doesn't work?

You want to know your grade in Computer Science, so write a program
that continuously takes grades between 0 and 100 to standard input
until you input "stop", at which point it should print your average to
standard output.
NOTE: When reading the input, do not display a prompt for the user.
Use the input() function with no prompt string. Here is an example:
grade = input()
grade = input()
count = 0
sum = 0
while grade != "stop":
grade = input()
sum += int(grade)
count += 1
print(sum / count)
Please dont solve it for me, but if you can point out why setting grade as "input()" doesnt work

You input a line as the first operation and then correctly enter the loop only if it isn't "stop".
However, that should then be the value you use for summing rather than immediately asking the user for another value. In your current code, if the user enters "stop", there is no check before attempting to treat it as a number.
So, if you don't want a solution, I'd suggest you stop reading at this point :-)
Couldn't resist, could you? :-)
The solution is to simply move the second input call to the bottom of the loop, not the top. This will do the check on the last thing entered, be that before the loop starts or after the value has been checked and accumulated.
In addition, your print statement is inside the loop where it will print after every entry. It would be better
There's other things you may want to consider as well, such as:
moving your print outside the loop since currently you print a line for every input value. You'll also have to catch the possibility that you may divide by zero (if the first thing entered was "stop").
handling non-numeric input that isn't "stop";
handling numeric input outside the 0..100 range.
Don't use this since you're trying to educate yourself (kudos on you "please don't solve it for me" comment by the way) and educators will check sites like SO for plagiarism, but a more robust solution could start with something like:
# Init stuff needed for calculating mean.
(count, total) = (0, 0)
#Get first grade, start processing unless stop.
grade = input()
while grade != "stop":
# Convert to number and accumulate, invalid number (or
# out of range one) will cause exception and not accumulate.
try:
current = int(grade)
if current < 0 or current > 100:
throw("range")
# Only reaches here if number valid.
total += int(grade)
count += 1
except:
print(f'Invalid input: {grade}, try again')
# Get next grade and check again at loop start.
grade = input()
# If we entered at least one valid number, report mean.
if count > 0:
print(total / count)

the first input does not work, covered by the second input;
when input is "stop", int("stop") is wrong;
When reading the input, do not display a prompt for the user. you should print the ans after the while loop
you can use endless loop and break to solve this problem.
...
while True:
grade = input()
if grade == 'stop':
break
...
print(ans)

Any way of returning 2 objects from a function without making a tuple?

I am making a basic date converter and I need to update the the date every time the user enters an invalid date and is asked to input again. From this function below, I need both the object day and year returned.
def day_valid (month, dates, feb_day, month_days):
day = int(dates[2:4])
while month_days == 31 and day > 31:
print ("Invalid day input.")
print()
dates = input_date()
day = int(dates[2:4])
if month_days == 31 and day < 32:
break
while month_days == 30 and day > 30:
print ("Invalid day input.")
print()
dates = input_date()
day = int(dates[2:4])
if month_days == 30 and day < 31:
break
while month_days == feb_day and day > feb_day:
print ("Invalid day input.")
print()
dates = input_date()
day = int(dates[2:4])
if month_days == feb_day and day <= feb_day:
break
return day
When a user types in 00102002 in MMDDYYYY format, there is no month. So the user is prompted to enter again, entering 01102005. The code still displays the date as 10 January 2002 and not 2005 .
If any one needs clarification on the code, please ask!
My main function:
def main():
loop = "Y"
print()
print("Welcome to Date Converter!")
print()
while loop.upper () == "Y" :
dates = input_date()
year = int(dates[4:])
month = month_valid(dates)
feb_day = feb_days(year)
month_days = month_Days(month, feb_day)
day = day_valid(month, dates, feb_day, month_days)
month_str = month_names(month)
print()
print("The date is " + str(day) + " " + month_str + " " + str(year))
loop = str(input ("Do you want to re-run this program? Y/N: "))
main()

This sounds first of all like an XY Problem: someone wants to do X, and comes up with a solution requiring doing Y. They need help with Y, so request help to do Y. However, it turns out that Y is not an appropriate solution. By recognizing the XY Problem and asking how to do X instead, the person gets better help and more insight into X.
XY Problems also often look suspiciously like homework problems, since those are often of the form "write a program that does X, by doing Y".
It's OK to pose a question that you want to do X and tried to solve it using Y.
Anyway, that's why you're probably going to get low-effort answers. I'll make the effort :)
Anyway, going with the Y question :)
There is a readability practice that considers tuples harmful because you don't know what the purpose of the items in the tuple are. Consider instead creating an object that holds the things, each with its own attribute, and then return that.
Since you stated that you needed day and year returned:
class DayAndYear(object):
def __init__(self, day, year):
self.day = day
self.year = year
And that's how you do it without making a tuple, and it increases the readability of your program, such as it is.
Now, going with the unstated X question:
without knowing what month_valid does,
assuming feb_days returns the number of days in February of the given year,
assuming month_Days returns the number of days in the given month when it isn't February,
it seems that you want a function that will check if a string is a valid MMDDYYYY string.
def is_valid_date(s):
"""Checks if the given date is a valid MMDDYYYY string.
Args:
s (str): A date to check.
Returns:
bool: True if the date is valid, False otherwise.
"""
if len(s) != 8:
return False
try:
date = int(s[:2])
month = int(s[2:4])
year = int(s[4:])
except ValueError:
return False
if month < 1 and month > 12:
return False
if month == 2:
days_in_month = days_in_february(year)
else:
days_in_month = days_in_month(month)
return date >= 1 and date <= days_in_month
def print_date(s):
"""Prints the given MMDDYYYY date, assuming it has already been checked for validity.
Args:
s (str): A date to print.
"""
print("The date is {:d} {:s} {:d}.".format(
int(s[2:4]), month_name(int(s[:2])), int(s[4:])))
I'd like to highlight a few general techniques to make your programs read better:
We don't know X. A well-posed question is one with specifications for the input and output of the program.
I've used verbose, readable function names.
I've used function comments, complete with args, arg types, and return values so there's no guessing about what things do.
I've chosen a split between checking validity and printing an already valid string. You can combine them. You can also return a string rather than print the date, and return instead the sentinel value None if the date was not valid.
Don't compute any more than you have to. Note the early returns.
No doubt there are library functions that will do this, but I've assumed you don't want to use any library functions.
The short key concepts:
Readability: Programs should be almost as easy to read as prose in your native language.
Readability: Function names should be descriptive.
Readability: Comment your code.
Readability: Choose a consistent format for functions and stick with it ("month_Days" vs "feb_days")
Efficiency: Return early.
Testability: Specify well what your program does in terms of inputs and outputs, give examples of good and bad inputs.
Effectiveness: Use library functions.
Stackoverflowness: Consider if your problem is an XY problem.

How to match input with elements in list/dictionary in Python3

I'm very new at coding, and I'm trying to create a shop list with items and prices on it.
That is, once typed in all the items, the function should calculate the sum and stop the moment you exceed the budget.
So I wrote something like:
def shoplist():
list={"apple":30, "orange":20, "milk":60......}
buy=str(input("What do you want to purchase?")
If buy in list:
While sum<=budget:
sum=sum+??
shoplist ()
I really don't know how to match the input of an item with the price in the list...
My first thought is to use 'if', but it's kinda impractical when you have more than 10 items on the list and random inputs.
I'm in desperate need of help....So any suggestions would be nice!! (or if you have a better solution and think me writing it this way is complete garbage... PLEASE let me know what those better solutions are😭😭😭

The code you post will not run in python. list is a builtin and should not be used for a variable name, and is doubly confusing since it refers to a dict object here. input() already returns a str so the cast has no effect. if and while should be lowercase, and there is no indentation, so we have no way of knowing the limits of those statements.
There are so many things wrong, take a look at this:
def shoplist(budget):
prices = {"apple":30, "orange":20, "milk":60}
# Initialise sum
sum = 0
while sum <= budget:
buy = input("What do you want to purchase?")
# Break out of the loop if the user hts <RETURN>
if not buy: break
if buy in prices:
sum += prices[buy] # This gets the price
else:
print("Invalid item", buy)
shoplist(142)
So what have I changed? The budget has to come from somewhere, so I pass it in as a parameter (142, I made that up). I initialise the sum to zero, and I moved the while loop to the outside.
Notice as well lots of whitespace - it makes the code easier to read and has no effect on performance.
Lots of improvements to make. The user should be shown a list of possible items and prices and also how much budget there is left for each purchase. Note as well that it is possible to go over budget since we might only have 30 in the budget but we can still buy milk (which is 60) - we need another check (if statement) in there!
I'll leave the improvements to you. Have fun!

Take a look at this as an example:
# this is a dictionary not a list
# be careful not using python reserved names as variable names
groceries = {
"apple":30,
"orange":20,
"milk":60
}
expenses = 0
budget = 100
cart = []
# while statements, as well as if statements are in lower letter
while expenses < budget:
# input always returns str, no need to cast
user_input = input("What do you want to purchase?")
if user_input not in groceries.keys():
print(f'{user_input} is not available!')
continue
if groceries[user_input] > budget - expenses:
print('You do not have enough budget to buy this')
user_input = input("Are you done shopping?Type 'y' if you are.")
if user_input == 'y':
break
continue
cart.append(user_input)
# this is how you add a number to anotherone
expenses += groceries[user_input]
print("Shopping cart full. You bought {} items and have {} left in your budget.".format(len(cart), budget-expenses))

I've made some changes to your code to make it work, with explanation including using comments indicated by the # symbol.
The two most important things are that all parentheses need to be closed:
fun((x, y) # broken
fun((x, y)) # not broken
and keywords in Python are all lowercase:
if, while, for, not # will work
If, While, For, Not # won't work
You might be confused by True and False, which probably should be lowercase. They've been that way so long that it's too late to change them now.
budget = 100 # You need to initialize variables before using them.
def shoplist():
prices = { # I re-named the price list from list to prices
'apple' : 30, # because list is a reserved keyword. You should only
'orange' : 20, # use the list keyword to initialize list objects.
'milk' : 60, # This type of object is called a dictionary.
} # The dots .... would have caused an error.
# In most programming languages, you need to close all braces ().
# I've renamed buy to item to make it clearer what that variable represents.
item = input('What do you want to purchase? ')
# Also, you don't need to cast the value of input to str;
# it's already a str.
if item in prices:
# If you need an int, you do have to cast from string to int.
count = int(input('How many? '))
cost = count*prices[item] # Access dictionary items using [].
if cost > budget:
print('You can\'t afford that many!')
else:
# You can put data into strings using the % symbol like so:
print('That\'ll be %i.' % cost) # Here %i indicates an int.
else:
print('We don\'t have %s in stock.' % item) # Here %s means str.
shoplist()
A lot of beginners post broken code on StackOverflow without saying that they're getting errors or what those errors are. It's always helpful to post the error messages. Let me know if you have more questions.

How To Print Strings Between Integer Ranges - Python 3

I'm very new to Python and programming in general, so excuse me if the code is terrible and the problem rather easy to solve.
I have written code to allow a user to have employee data printed based on 3 different inputs, which they are allowed to choose from.
The options the user has available to them are to pick employees based on their payroll number; a minimum and maximum salary range; their job title.
I made two functions for the formatting. The first one turns the lines of the text file into lists, then the second function grabs those individual lists and formats them.
Then the code requests the user to input the file name. If the file cannot be found, they get to try again. If it is correct, the file is loaded and then runs through the functions to print out a neat table.
Then the user is asked what method they want to choose from to select specific employees. They are given 4 options, 3 are mentioned at the start and the fourth is to just end the program.
I managed to successfully get the first option to print out the employees without hassle, as is the same for the fourth option to end the program. I almost have the third one completed, I just need to find a way to print the name without a comma. My problem resides within the second option: how do I print the employees and their details if they fall between the minimum and maximum salary ranges entered by the user if the range isn't an integer since it has to include a '£' sign?
Here's the code. It's the biggest chunk in the program because I just have no clue how to make it work properly -
def detailsPrint(field) : #takes tuple and prints
print("{:30}" "{:6}" "{:15}" "{:7}".format(field[3] + ", " + field[4], field[0], field[2], "£" + field[1]))
if display == 2 :
maxSalary = "£1000000"
minpay = input("Enter the minimum pay : ")
maxpay = input("Enter the maximum pay : ")
if len(minpay) and len(maxpay) < maxSalary :
for s in employeeList :
if s[1] >= minpay :
detailsPrint(s)
The outcome should be something like (example) Simpson, Bart 12345 Consultant £55000 if the minpay were to be £50000 and maxpay £60000
edit: Managed to get it working. Here's the code
if display == 2 :
x = False
maxSalary = 1000000
minpay = int(input("Enter the minimum pay: "))
maxpay = int(input("Enter the maximum pay: "))
if int(minpay) > int(maxSalary) or int(maxpay) > int(maxSalary) :
x = False
print("No employees earn over £1000000. Try again.")
if int(minpay) or int(maxpay) < int(maxSalary) :
for s in employeeList :
if int(s[1]) >= minpay and int(s[1]) <= maxpay :
detailsPrint(s)
x = True
if x == False :
print("No employees could be found within that range. Try again")
print("\n")

Simplest solution: don't ask for the £ char ;-)
A solution that work with your requirement is to change the line
if len(minpay) or len(maxpay) > maxSalary :
with something like
if int(minpay[1:]) > int(maxSalary[1:]) or int(maxpay[1:]) > int(maxSalary[1:]) :
which check the numeric value of the strings (your condition seems wrong anyway to me)

You could replace all "£" signs to "" in a string.
YourString.replace("£", "")

How to do the correct casting using a loop in python?

The objective is to write a program that will increase the population every 7 and 35 seconds and decrease every 13 seconds. I am trying to use a loop for this program and I am having some problems with getting the right casting for each variable. Here's the code:
#(1)There is a birth every 7 seconds (2)There is a death every 13 seconds (3)There is a new
immigrant every 35 seconds.
#CURRENT POP: 307,357,870
populationCurrent = input("What is the current population")
x=0
while x!=100:
if (x%7==0):
populationCurrent=populationCurrent+1
x=x+1
elif (x%13==0):
populationCurrent=populationCurrent-1
x=x+1
elif (x%35==0):
populationCurrent+=1
x=x+1
else:
x=x+1
print("The population will be "+int(populationCurrent)+".")
Thank you for your time.

I think you are confused in python2 and python3, there's a difference in input() function of python 2.x and python 3.x, where input() function gives an integer value in python 2 and str in python 3

input() is str by default so, this should be converted to int
populationCurrent = str(input("What is the current population"))
You cannot concatenate string and int
print("The population will be "+str(populationCurrent)+".")
Its easier to do this than iterate through 100 times
populationCurrent += 100//7 + 100//35 - 100//13

You need to convert populationCurrent to an integer immediately after you read the string.
populationCurrent = int(input("What is the current population"))
Note that if you don't enter a string that is a valid integer representation, this will raise a ValueError. You might want to consider how to handle that (catch it and use a default value? catch it and try to read another value? Let the exception propagate?)
With this change, you'll have to convert the integer value back to a string for the output:
print("The population will be "+str(populationCurrent)+".")
or using any of the various string formatting tools available. It's better to have populationCurrent as an integer, since there are more places in your code that assume it to be an integer than assume it to be a string.

The only thing you need to do is convert populationCurrent from string to int:
populationCurrent = int(input("What is the current population?"))
The more concerning stuff is that your code doesn't do what it's supposed to: when x is 35 you will only have one birth, since 35 % 7 is 0, but no immigrant will arrive. Do something like this, removing the elif statements which do not make the code that more efficient anyway:
while x!=100:
if (x%7==0):
populationCurrent=populationCurrent+1
if (x%13==0):
populationCurrent=populationCurrent-1
if (x%35==0):
populationCurrent+=1
x=x+1
print("The population will be ", populationCurrent, ".")
Though still note that the loop will stop after x gets to 100. You could reset it but I don't know for how long you want it to run.

def intInput(prompt):
while 1:
try: return int(input(prompt))
except ValueError: print("Invalid Input!")
def YearToModifier(x):
if x%35 ==0 or x%7 ==0: return 1
if x%13 == 0: return -1
return 0
populationCurrent = intInput("What is the current population?") #ensure you get an int
n_years = intInput("How Many Years?") #ensure you get an int
#in this case populationChange is independent of initial population (this is rarely the case in reality)
populationChange = sum(YearToModifier(x) for x in range(n_years))
#the population in the future is the initialPopulation + population Change ... duh...
populationFuture = populationCurrent + populationChange
print("The Population will be %d!"%populationFuture)
there you go
WRT #martjinpeters comment on OP you could change YearToModifier to
def YearToModifier(x):
return sum([x%35 ==0,x%7 ==0,-1*int(x%13 == 0)])
of coarse as #AshokaLella points out you can calculate the total births/immigrations/deaths for a given number of years without actually visiting each year
births = n_years//7
immigrations = n_years//35
deaths = n_years//13
populationChange = births + immigrations - deaths