title: python warnings saying "Name "X" can be undefined"
body: <p>I am pretty new to programming and I have made an app which works fine but I get warnings saying "Name "X" can be undefined". What does this mean and how could I get rid of the warning? I am using Python 3.8 with Intelij IDE 2020.1. </p>
  
  <p>Here is a screenshot of my issue:</p>
  
  <p><a href="https://i.stack.imgur.com/Be1Rq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Be1Rq.png" alt="enter image description here"></a></p>
  
  <p>Here is a minimum repo of my code:</p>
  
  <pre><code>print("1. school a \n2. school b")
  while True:
      try:
          school_number = int(input("\nEnter the number of what school you are at: "))
          break
      except ValueError:
          print("That was an invalid number.  Please try again...\n")
  
  current_day = input("Please enter what day it is (mon/tue etc): ".lower())
  
  if school_number == 1:
      school_name = "school A"
      cost = (7.50 * 2)
      leave_time_multiplier = 1.15
      if current_day == "mon":
          start_time = 09.30
          finish_time = 14.30
      else:
          pass
  
  if school_number == 2:
      school_name = "school B"
      cost = (9.50 * 2)
      leave_time_multiplier = 1.25
      if current_day == "mon":
          start_time = 17.00
          finish_time = 20.30
      else:
          pass
  
  # renames the days
  if current_day == "mon":
      day = "Monday"
  else:
      day = "Other"
  
  leave_time = start_time - leave_time_multiplier - 1
  
  print("\nOn {} at {}: It will cost {:.2f} return. You start at {:.2f} and finish at {:.2f} You should leave at"
        "{:.2f}".format(day, school_name, cost, start_time, finish_time, leave_time))
  </code></pre>