Standard Output and Input

Standard Output

The most common way to output something is using print function:

print(2 * 3)
print("hello")
arr = [1, 2, 3, 4]
print(arr)

Output:

6
hello
[1, 2, 3, 4]

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Or you can use sys.stdout.write:

from sys import stdout
arr = [1, 2, 3, 4]
stdout.write("hello ")
stdout.write(str(arr))

Output:

hello [1, 2, 3, 4]

Standard Input

To get user input, you can use the input function:

name = input("What's your name?")
print "hello", name

Change from Python2

The raw_input function from Python2 is no longer supported in Python3. The input() function in Python3 works the same way as the raw_input() function in Python2.

The input() function in Python3 always returns a String. You must cast the variable to use the variable as a different type.

num = input("Give me a number")
print(num)               # 12
print(num * 2)           # 1212

# now convert it to number
num = int(num)
print(num * 2)           # 24

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You can also read user's input by using sys.stdin.read or sys.stdin.readline:

from sys import stdin

name = stdin.readline()
print(name)

# Only reads 3 characters
name = stdin.readline(3)
print(name)