Can anyone take the time to explain to a complete newbie why this wont print? Thanks.
‘’’
weight_lbs = input('What is your weight? ')
weight_kg = int(weight_lbs)*.45
print(weight_kg + ’ kg ‘)
‘’’
It returns TypeError: unsupported operand type(s) for +: ‘float’ and ‘str’
Reading and understanding error messages is importan skill. This is quite self-explanatory: what should happen if you try add float (weight_kg) and str (‘kg’)? I don’t know, neither does Python.
To overcome this I suggest of using f-strings:
print(f"Your weight is {weight_kg} kg")As per the above post, or do a type conversion in the print() function:
print(str(weight_kg) + " kg")
print(weight_kg + ’ kg ')
The print() function will coerce parameters into a string before it
writes them to your display, but in this case you’re passing an
expression as a single argument:
weight_kg + ' kg '
That’s where the error comes from. You can’t add a floating point
number and a string to one another. There are a few ways around
this… you could simply make them separate arguments to the print()
function so that it will convert the float to a str for you:
print(weight_kg, 'kg')
Or you could recast the float to a str yourself in the argument:
print(str(weight_kg) + ' kg')
Or you could use string formatting to inject the float into a
template:
print('%f kg' % weight_kg)
Or you could use an f-string if you have a new enough Python
interpreter:
print(f'{weight_kg} kg')
I could probably list half a dozen more ways, but it all comes down
to either solving your invalid expression before passing it to the
function, or splitting it into multiple expressions which
individually work as arguments to the function.
thanks all. Really appreciate the rapid responses, I will try and understand what you have all been so kind to share…
Welcome to Python! It’s a very fun language.
One of the cool things about Python is that you can change the type of thing you have inside your variable. For example, this is valid code:
# This variable is an integer
my_var = 45
# Now it's a float
my_var = 45.0
#Now it's a string
my_var = '45'
In some languages, the type (the sort of data) a variable holds can’t change over the course of your program. That is, if my_var started out holding an integer, you couldn’t make it hold a string later.
But Python will let you change the type of your variables (e.g. change what sort of data your variable holds). Because of that, Python sometimes has to use context clues to figure out what to do.
In this code:
x = 2
y = 3
print(x+y)
Both x and y are integers, so it’s obvious that you want to add them together. Running this code will print 5.
By the same token if you have this code:
x = 'apples and'
y = ' oranges'
print(x+y)
Python knows that both x and y are strings, so it’s obvious you want to concatenate (smoosh) them together. Running this code will print 'apples and oranges'.
But what happens when you mix up variables? What if you have this code:
x = 2
y = ' oranges'
print(x+y)
What’s Python supposed to do now? The integer (x) suggests you want arithmetic, but the string (y) suggests you want concatenation. It can’t read your mind so it throws an error: TypeError: unsupported operand type(s) for +: 'int' and 'str'. What does that mean?
Let’s break down the error message.
Okay, so how can you fix it? Does that mean you can never mix numbers and text? That wouldn’t be very useful.
In order to get around this, you just have to convert one type of variable to the other. In this example, there’s no number equivalent to the word ‘oranges’, so that means we’ll have to convert the number to a string. You can do it this way:
x = 2
y = ' oranges'
print(str(x)+y)
Now, you get 2 oranges.
I hope this gets you started! One other note–you were really close, but you used an apostrophe and a quotation mark to try and surround your code. It’s three backticks, the little accent looking things above the Tab key on an English QWERTY keyboard. That’s how you make it look like code.