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Part 3 Python 3 Data Types and Processing 3.1 Data types 3.2 Number processing 3.3 String Processing 3.4 Converting one type to another A variable is a name that refers to a value. The assignment
statement creates new variables and gives them values: word = "spam" Every object has a data type (e.g. string) , a size (in bytes), a value
(e.g. "spam" ) and a location in the
computer's memory.
. . A variable name is a reference Please note: all Python 3
example programs can be found here:
# program 03-01.py total = 10 print (total) print (type
(total)) How to get help on the Python Language When you start to use the Python
language, you may want to get more information on features such as type , which allows you to inspect the data type
of an object. . . Python Help Python has its own Help system:
When in the Python Shell (interactive) window, at the >>> prompt, type: help() Read the instructions provided.
The example programs shown here: contain useful comments to help you understand what the programs
are doing.
Please carefully read the following
important document...
Python's Data Types The main data types in Python are
numbers and strings (i.e. text). int (integer, e.g. 12, 14, -101) float (floating point, e.g. 3.142, 98.6) string (text, e.g. "Anne", 'Anne',
"Hello World!") int a minimum of 32 bits (4 bytes)
to unlimited precision float 64 bits (8 bytes) precision (precision machine
dependent) string regular
ASCII code strings are 1 byte per character Python Data Types and Processing
3.1 Data types 3.2 Number processing 3.3 String Processing 3.4 Converting one type to another Numeric
Expressions (int) # See program 03-04.py
2 + 4 6 - 4 6 * 3 6 / 3 6 % 3 # % is the modulus operator - see below for more info 6 // 3 # floor division:
always truncates fractional remainders -5 3**2 # three to the
power of two The % (modulus or modulo) operator yields the remainder
from the division of the first argument by the second. The arguments may be
floating point numbers, e.g., 3.14
% 0.7 equals 0.34 (since 3.14
equals 4 * 0.7 + 0.34.),
or integer numbers, e.g., 5 % 2 equals 1 (since 5 equals 2
* 2 + 1.).
Click here for info on
when you might want to use the modulus operator.
Numeric
Expressions (float)
# See program 03-05.py
2.0 + 4.0 6.0 - 4.0 6.0 * 3.0 6.0 / 3.0 6.0 % 3.0 # % is the modulus operator - see below for more info 6.0 // 3.0 # floor
division: always truncates fractional remainders -5.0 3.0**2.0 # three to the
power of two
The % (modulus or modulo) operator yields the remainder
from the division of the first argument by the second. The arguments may be
floating point numbers, e.g., 3.14
% 0.7 equals 0.34 (since 3.14
equals 4 * 0.7 + 0.34.),
or integer numbers, e.g., 5 % 2 equals 1 (since 5 equals 2
* 2 + 1.).
Click here for info on
when you might want to use the modulus operator.
Mixed
Numeric Expressions # See program 03-06.py
2 + 4.0 6 - 4.0 6 * 3.0 6 / 3.0 6 % 3.0 # % is the modulus operator - see below for more info 6 // 3.0 # floor division:
always truncates fractional remainders -5.0 3**2.0 # three to the
power of two The % (modulus or modulo) operator yields the remainder
from the division of the first argument by the second. The arguments may be
floating point numbers, e.g., 3.14
% 0.7 equals 0.34 (since 3.14
equals 4 * 0.7 + 0.34.),
or integer numbers, e.g., 5 % 2 equals 1 (since 5 equals 2
* 2 + 1.).
Click here for info on
when you might want to use the modulus operator.
# See program 03-07.py
7 > 10 # 7 is greater than 10 -
this expression has the value "false" 4 < 16 # 4 is less than 16 - this
expression has the value "true" 4 == 4 # 4 is equal to 4 - this expression has the value "true" 4 <= 4 # 4 is less than or equal to 4 - this expression has the value
"true" 4 >= 4 # 4 is greater than or equal to 4 - this expression has the value
"true" 4 != 4 # 4 is not equal to 4 - this expression has the value
"false" Boolean
expressions result in values true or false
# See program 03-07.py
7 > 10 4 < 16 4 == 4 4 <= 4 4 >= 4 4 != 4
In expressions where there are a number of
different operators, do some have precedence over others? Yes they do... For example,
multiplications are always done before additions and subtractions.
Click here for more
important information on operator precedence .
Python Data Types and Processing
3.1 Data types 3.2 Number processing 3.3 String Processing 3.4 Converting one type to another Python's Data Types The main data types in Python are
numbers and strings (i.e. text). int (integer, e.g. 12, 14, -101) float (floating point, e.g. 3.142, 98.6) string (text, e.g. "Anne", 'Anne',
"Hello World!") String Objects string text, e.g. "Anne" 'Anne' "where's the
spam?" # See program 03-08.py # See program 03-09.py
String Assignments a = "Hello out there" print (a) b = 'Hello' print (b) c = "Where's the spam?" print (c) d = 'x' print (d)
String Concatenation (joining) # See program 03-10.py
a = 'Hello out there' b = "Where's the spam?" c = a + b print (c)
Click here for more
info on the + operation.
Python Data Types and Processing
3.1 Data types 3.2 Number processing 3.3 String Processing 3.4 Converting one type to another Converting one data type to another (int to str) # See program 03-11.py
a = 'Hello out there' b = "Where's the spam?" c = a + b print (c) #d = c + 10 # you cannot concatenate a string and an integer # you must convert the integer to a string first: d = c + str(10) print (d)
Click on the following link to see how
to use the + operator to join together
(concatenate) two strings or add together two numbers:
http://www.annedawson.net/Python_Plus_Operator.html
Converting one data type to another (str to int)
# See program 03-12.py
a = "10" b = '99' c = a + b print (c) print (type(c)) c = int(c) print (c) print (type(c))
Rounding a floating point number to the
nearest integer # See program 03-13.py
# 03-13.py
# How to round up a
floating point number
# to the nearest
integer
# Updated: Monday
24th January 2011, 16:24 PT, AD
x = 1.6
print (x)
x = round(x)
print (x)
#compare the above
with
x = 1.6
x = int(x)
print (x)
This Presentation uses the following program files: 03-01.py 03-02.py 03-03.py 03-04.py 03-05.py 03-06.py 03-07.py 03-08.py 03-09.py 03-10.py 03-11.py 03-12.py 03-13.py
Please note: all Python 3
example programs can be found here:
VIDEO
End of Python3_Data_Types.htm