Python Programming/Variables
This lesson introduces variables, expressions, and statements.
Objectives and Skills
editObjectives and skills for this lesson include:[1]
- Language Basics
- Language elements (constants, numbers and strings)
- Strings types (single quotes, double quotes and triple quotes)
- Escape Sequence, string concatenation and format method
- Variables naming, types and objects
- Indentation, logical and physical lines
- Operators and Expressions
- Operators and Expressions
- Evaluation Order and Associativity
- Input Output
- User input
Readings
editMultimedia
editExamples
editData Types
editBuilt-in Python data types include integer (int), floating point (float), string (str), and Boolean (bool) data types.[2]
value = 1 + 1
print(value) # Displays 2
print(type(value)) # Displays <type 'int'>
value = 0.1 + 0.1
print(value) # Displays 0.2
print(type(value)) # Displays <type 'float'>
value = '1' + '1'
print(value) # Displays 11
print(type(value)) # Displays <type 'str'>
value = True
print(value) # Displays True
print(type(value)) # Displays <type 'bool'>
Type Conversion
editAn object’s type is accessed by the built-in function type().[3]
value = 1.9
print(value) # Displays 1.9
print(type(value)) # Displays <type 'float'>
value = int(value)
print(value) # Displays 1
print(type(value)) # Displays <type 'int'>
value = 1
print(value) # Displays 1
print(type(value)) # Displays <type 'int'>
value = float(value)
print(value) # Displays 1.0
print(type(value)) # Displays <type 'float'>
value = 1
print(value) # Displays 1
print(type(value)) # Displays <type 'int'>
value = str(value)
print(value) # Displays 1
print(type(value)) # Displays <type 'str'>
Quotes
editString literals are written in a variety of ways, including single quotes, double quotes, and triple quotes. Triple quoted strings may span multiple lines.[4] The backslash (\) character is used to escape characters that otherwise have a special meaning, such as newline, backslash itself, or the quote character.[5]
value = 'single quotes'
print(value)
value = "double quotes"
print(value)
value = \
'''triple quotes
span multiple lines'''
print(value)
value = '"nested quotes"'
print(value)
value = "'nested quotes'"
print(value)
value = "\"escape character quotes\nand multiple lines\""
print(value)
Numeric Operations
editAll numeric types (except complex) support the following operations, sorted by ascending priority.[6]
a = 3
b = 2
print(a + b) # 5
print(a - b) # 1
print(a * b) # 6
print(a / b) # 1.5
print(a // b) # 1
print(a % b) # 1
print(-a) # -3
print(a ** b) # 9
Assignment Operations
editAn assignment statement evaluates the expression and assigns the result to the target. Augmented assignment is the combination, in a single statement, of an operation and an assignment statement.[7]
a = 3
b = 2
a += b # a = 5
a -= b # a = 3
a *= b # a = 6
a /= b # a = 1.5
a //= b # a = 1
a %= b # a = 1.0
a **= b # a = 9
Input Function
editPython 2: If the prompt argument is present, it is written to standard output without a trailing newline. The function then reads a line from input, converts it to a string (stripping a trailing newline), which is then parsed and evaluated as a Python expression.[8]
Python 3: If the prompt argument is present, it is written to standard output without a trailing newline. The function then reads a line from input, converts it to a string (stripping a trailing newline), and returns that.[9]
input([prompt])
#Python 2
value = input("Enter a numeric value: ")
print("You entered " + str(value))
value = input('Enter a string value in "quotes": ')
print("You entered " + value)
#Python 3
value = input("Enter a value: ")
print("You entered a string value " + value)
Activities
editTutorials
edit- Complete one or more of the following tutorials:
- LearnPython
- TutorialsPoint
- Codecademy
- SoloLearn
- Wikiversity
- Wikibooks
Practice
edit- Experiment with different numeric operations to ensure you understand how they work. Then review either MathsIsFun: Order of Operations or Teachoo: What is BODMAS?. Create a Python program that demonstrates the order of operations.
- Create a Python program to prompt the user for hours and rate per hour to compute gross pay (hours * rate).[10]
- Review MathsIsFun: Conversion of Temperature. Create a Python program that asks the user for a Fahrenheit temperature and then calculate and display the corresponding Celsius temperature or ask the user for a Celsius temperature and then calculate and display the corresponding Fahrenheit temperature.
- Create a Python program that asks the user how old they are in years, and then calculate and display their approximate age in months, days, hours, and seconds.
- Review MathsIsFun: Area of Plane Shapes. Create a Python program that asks the user for the dimensions of different shapes and then calculate and display the area of the shapes.
Games
edit- Play CodeCombat.
Lesson Summary
edit- Built-in Python data types include integer (
int()
), floating point (float()
), string (str()
), and Boolean (bool()
).[11] - An object’s type is accessed by the built-in function
type()
.[12] - String literals are written in a variety of ways, including single quotes, double quotes, and triple quotes. Triple quoted strings may span multiple lines.[13]
- The backslash (
\
) character is used to escape characters that otherwise have a special meaning, such as newline, backslash itself, or the quote character.[14] - Numeric operators include
+
,-
,*
,/
,//
,%
, and**
.[15] - Assignment operators include
+=
,-=
,*=
,/=
,//=
,%=
, and**=
.[16] - The Python 2
input()
function reads a line from input, converts it to a string (stripping a trailing newline), which is then parsed and evaluated as a Python expression.[17] - The Python 3
input()
function reads a line from input, converts it to a string (stripping a trailing newline), and returns that.[18]
Key Terms
edit- assignment
- A statement that assigns a value to a variable.[19]
- concatenate
- To join two operands end to end.[20]
- comment
- Information in a program that is meant for other programmers (or anyone reading the source code) and has no effect on the execution of the program.[21]
- escape character
- A character which invokes an alternative interpretation on subsequent characters in a character sequence.[22]
- evaluate
- To simplify an expression by performing the operations in order to yield a single value.[23]
- expression
- A combination of variables, operators, and values that represents a single result value.[24]
- floating point
- A type that represents numbers with fractional parts.[25]
- floor division
- The operation that divides two numbers and chops off the fractional part.[26]
- integer
- A type that represents whole numbers.[27]
- keyword
- A reserved word that is used by the compiler to parse a program; you cannot use keywords like if, def, and while as variable names.[28]
- mnemonic
- A memory aid. We often give variables mnemonic names to help us remember what is stored in the variable.[29]
- modulus operator
- An operator, denoted with a percent sign (%), that works on integers and yields the remainder when one number is divided by another.[30]
- operand
- One of the values on which an operator operates.[31]
- operator
- A special symbol that represents a simple computation like addition, multiplication, or string concatenation.[32]
- rules of precedence
- The set of rules governing the order in which expressions involving multiple operators and operands are evaluated.[33]
- statement
- A section of code that represents a command or action. So far, the statements we have seen are assignments and print statements.[34]
- string
- A type that represents sequences of characters.[35]
- type
- A category of values. The types we have seen so far are integers (type int), floating-point numbers (type float), and strings (type str).[36]
- value
- One of the basic units of data, like a number or string, that a program manipulates.[37]
- variable
- A name that refers to a value.[38]
Review Questions
edit-
Built-in Python data types include _____, _____, _____, and _____.Built-in Python data types include integer (int()), floating point (float()), string (str()), and Boolean (bool()).
-
An object’s type is accessed by the built-in function _____.An object’s type is accessed by the built-in function type().
-
String literals are written in a variety of ways, including _____, _____, and _____. _____ may span multiple lines.String literals are written in a variety of ways, including single quotes, double quotes, and triple quotes. Triple quoted strings may span multiple lines.
-
The _____ character is used to escape characters that otherwise have a special meaning, such as _____.The backslash (\) character is used to escape characters that otherwise have a special meaning, such as newline, backslash itself, or the quote character.
-
Numeric operators include _____.Numeric operators include +, -, *, /, //, %, and **.
-
Assignment operators include _____.{{{2}}}
-
The Python 2 input() function _____.The Python 2 input() function reads a line from input, converts it to a string (stripping a trailing newline), which is then parsed and evaluated as a Python expression.
-
The Python 3 input() function _____.The Python 3 input() function reads a line from input, converts it to a string (stripping a trailing newline), and returns that.
Assessments
edit- Flashcards: Quizlet: Python Variables
- Flashcards: Quizlet: Python Variable Types
- Flashcards: Quizlet: Python Variables, Expressions, and Statements
- Quiz: Quizlet: Python Variables
- Quiz: Quizlet: Python Variable Types
- Quiz: Quizlet: Python Variable, Expressions, and Statements
See Also
edit- Python.org: An Informal Introduction to Python
- Python.org: Built-in Types
- Python.org: Expressions
- Python.org: Data model
- Python.org: Simple statements
- SoloLearn: Python
- Open Book Project: Python 3 - Variables, expressions and statements
- Digital Ocean: How to use Variables in Python 3
- PythonBasics: variables
References
edit- ↑ Vskills: Certified Python Developer
- ↑ Python.org Built-in Types
- ↑ Python.org: Built-in Types
- ↑ Python.org: Built-in Types
- ↑ Python.org: Lexical analysis
- ↑ Python.org: Built-in Types
- ↑ Python.org: Simple Statements
- ↑ Python.org: Built-in Functions
- ↑ Python.org: Built-in Functions
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ Python.org Built-in Types
- ↑ Python.org: Built-in Types
- ↑ Python.org: Built-in Types
- ↑ Python.org: Lexical analysis
- ↑ Python.org: Built-in Types
- ↑ Python.org: Simple Statements
- ↑ Python.org: Built-in Functions
- ↑ Python.org: Built-in Functions
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ Wikipedia: Escape character
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements
- ↑ PythonLearn: Variables, expressions, and statements