input()
and Standard In
A program that runs in the terminal is called a "console program" (console and terminal are practically synonyms). These console programs can become much more interactive if we learn a way for the user to give us some "input". Python has a simple function for doing so, the aptly named input
function.
def hello(): print('hello there') user_status = input('how are you? ') print('you said: ' + user_status) def main(): hello()
Input in the Terminal
Here is example of running the above hello.py
in the terminal. In this example the text written by the user is in blue.
$ python3 hello.py
hello there
how are you? I am fine
you said: I am fine
Changing variable types
When you call the input
function, the response entered by the user is given back to you! It is always "returned" as a value of type "str" also known as a string. That is a problem if you want to do any further computation. For example, lets say you wanted to print the value a user entered divided by two:
>>> x = input('enter a value: ')
enter a value: 42
>>> print(x)
42
>>> print(x/2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for /: 'str' and 'int'
This is subtle, but recall that every variable has a type. Even though x looks like a number, its type is string. Recall that input always returns a string. The interpreter is complaining that it doesn't make sense to divide a string! Now that you know what the issue is, the fix is simple. You just need to change the variable type to be a float or an int. To do so you can use functions called float
and int
.
>>> x_float = float(x) >>> print(x_float/2) 21.0We can call x_float anything we like. I put the term "float" in the name simply so that you can understand the type just by reading the name.