Python Conditional tests with lists (cont.)

Python Conditional tests with lists (cont.)



Conditional tests with lists (cont.)

#Testing if a value is not in a list
banned_users = ['ann', 'chad', 'dee']
user = 'erin'

if user not in banned_users:
 print("You can play!")
#Checking if a list is empty
player = []

if players:
 for player in players:
   print("player:" + player.title())
else:
 print("we have no players yet!")

Screenshot 

python list test

 


Accepting Input
You can allow your users to enter input using the input() statement. In Python 3, all input is stored as a string.

#Simple input 
name = input ("what's your name? ")
print("Hello, " +name + ".")
#Accepting numerical input
age = input("How old are you? ")
age = int(age)

if age >= 18:
 print("\nYou can vote!")
else:
 print("\nYou can't vote yet.")


Screenshot 

python input

 


While loops
 A while loop repeats a blocks of code as long as a condition is True.

#Counting to 5
current_number =1

while current_number <= 5:
 print(current_number)
 current_number += 1

Screenshot 

python while loop

 

while loops (cont.)

#Letting the user choose when to quit

prompt = "\nTell me something, and I'll "
prompt += "repeat it back to you."
prompt += "\n Enter 'quit' to end the program. "



message = ""
while message != 'quit':
	message = input(prompt)

if message != 'quit':
	print (message)
#Using a flag
prompt = "\nTell me something, and I'll "
prompt += "repeat it back to you."
prompt += "\n Enter 'quit' to end the program. "

active= True
while active:
	message = input(prompt)

if message == 'quit':
	active = False
else:
	print (message)

#Using break to exit a loop
prompt = "\nWhat cities have you visited?"
prompt += "\n Enter 'quit' when you're done. "

while True:
	city = input (prompt)
	if city == 'quit':
		break
	else:
		print("I've been to " + city + "!")

Screenshot 

python infinite loop

 


Accepting input with Sublime Text

Sublime Text doesn't run programs that prompt the user for input. You can use sublime Text to write programs that prompt for input, but you'll need to run these programs from a terminal.

Breaking out of loops

You can use the break statement and the continue statement with any of python's loops. For example you can use break to quit a for loop that's working through a list or a dictionary. You can use continue to skip over certain items when looping through a list or dictionary as well.

while loops(cont.)

#Using continue in a loop
banned_users = ['eve', 'fred', 'gary', 'helen']

prompt = "\n Add a player to your team."
prompt += "\n Enter 'quit' when you're done. "

players = []
while True:
	player = input(prompt)
	if player == 'quit':
		break
	elif player in banned_users:
		print(player + " is banned!")
		continue
	else:
		players.append(player)

print("\nYour team:")
for player in players:
	print(player)


Screenshot 

python continue

 

Avoiding infinte loops

Every while loop needs a way to stop running so it won't continue to run forever. If there's no way for the condition to become False, the loop will never stop running.

#An infinite loop
while True:
	name = input("\nWho are you? ")
	print("Nice to meet you, " + name + "!")

Screenshot 

python infinte

 


Removing all instances of value from a list

The remove() method removes a specific value from a list, but it only removes the value you provide. You can use a while loop to remove all instances of a particular value.

#Removing all cats from a list of pet
pets = ['dog', 'cat', 'dog', 'fish', 'cat', 'rabbit', 'cat']
print(pets)

while 'cat' in pets:
	pets.remove('cat')

print(pets)

Screenshot 

python list

 

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