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First steps in Python
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Python is a textual programming language used by beginners and by professionals. You type the instructions, and spelling and punctuation matter.
Output with print
print shows something on the screen.
print("Hello, world!")
Text in quotes is a string. Numbers do not need quotes: print(5 + 2) shows 7.
print("Hello, world!")
Text in quotes is a string. Numbers do not need quotes: print(5 + 2) shows 7.
Variables
A variable is a named box that stores a value. = puts a value into it.
name = "Sam"
age = 12
print("Hello", name)
print(age + 1)
Output:
Hello Sam
13
Variable names cannot contain spaces or start with a number. Use names that explain the data, such as score.
name = "Sam"
age = 12
print("Hello", name)
print(age + 1)
Output:
Hello Sam
13
Variable names cannot contain spaces or start with a number. Use names that explain the data, such as score.
Input and data types
input reads what the user types. It always gives a string.
name = input("Your name? ")
To do maths with typed numbers, convert with int() for whole numbers:
age = int(input("Age? "))
Watch out: "3" + "4" joins strings to make 34, but 3 + 4 is 7.
name = input("Your name? ")
To do maths with typed numbers, convert with int() for whole numbers:
age = int(input("Age? "))
Watch out: "3" + "4" joins strings to make 34, but 3 + 4 is 7.
What does this program print?
x = 5
x = x * 2
x = x - 3
print(x)
- x starts as 5.
- x = 5 * 2 = 10.
- x = 10 - 3 = 7.
Answer: 7
print shows output, = stores a value in a variable, input reads text from the user and int() turns it into a whole number. Strings in quotes join together; numbers add.
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