And now for something completely different . . .

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And now for something completely different . .
.
2

• Part 3
• Python Data Types
• and
• Processing

3
PythonData Types and Processing

• 3.1 Data types
• 3.2 Number processing
• 3.3 String Processing
• 3.4 Converting one type to another

4
PythonData Types and Processing

• 3.1 Data types
• 3.2 Number processing
• 3.3 String Processing
• 3.4 Converting one type to another

5
A variable is a name that refers to a value. The
assignment statement creates new variables and
gives them valuesword "spam"print word
Variables in Python
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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. . .
Variables refer to Objects
Variable names such as word or sum actually
correspond to Python objects.
7
Creation of a numeric variable
sum 10
sum
10
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A variable name is a reference
A variable name is a reference to an object. In
the following diagram, the object is shown as the
orange box. The size of the box is measured in
bytes.
sum 10
10
The value of the object is 10. The type of the
object is int.
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A variable name is a reference
A variable name is a reference to an object.
Variables are said to refer to (point to) the
object.
sum
Variable names actually store the address of the
location of the object in memory.
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You don't need to know that
address.
By using a variable's name you gain access to the
value stored at that address.
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• http//www.annedawson.net/PythonPrograms.txt
• 03-01.py
• sum 10

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http//www.annedawson.net/PythonPrograms.txt 03-02
.py

• sum 10
• print sum

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http//www.annedawson.net/PythonPrograms.txt 03-03
.py

• sum 10
• print sum
• print type (sum)

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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. . .

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Python Help

• Python has its own Help system
• http//www.annedawson.net/Python_Help.htm

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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. 3.142e-10, 98.6)
• string (text, e.g. "Anne", 'Anne', "Hello
  World!")

There are other data types (e.g. lists,
dictionaries, files) which will be introduced
later in the course.
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Storage Requirements of the Data types

• int (integer, e.g. 12, 14, -101)
• float (floating point, e.g. 3.142e-10, 98.6)
• string (text, e.g. "Anne", 'Anne', "Where's the
  spam?")

How many bytes of memory do objects of the
different types occupy?
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Storage Requirements of the Data types

• 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

See the notes on the next slide taken from
the official Python web site...
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Python Library Reference2.3.4 Numeric Types

• There are four distinct numeric types plain
  integers, long integers, floating point numbers,
  and complex numbers. In addition, Booleans are a
  subtype of plain integers. Plain integers (also
  just called integers) are implemented using long
  in C, which gives them at least 32 bits of
  precision. Long integers have unlimited
  precision. Floating point numbers are implemented
  using double in C. All bets on their precision
  are off unless you happen to know the machine you
  are working with.

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PythonData Types and Processing

• 3.1 Data types
• 3.2 Number processing
• 3.3 String Processing
• 3.4 Converting one type to another

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Numeric Expressions (int)

• 2 4
• 6 - 4
• 6 3
• 6 / 3
• 6 3
• 6 // 3
• -5
• 32

03-04.py
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Numeric Expressions (float)

• 2.0 4.0
• 6.0 - 4.0
• 6.0 3.0
• 6.0 / 3.0
• 6.0 3.0
• 6.0 // 3.0
• -5.0
• 3.02.0

03-05.py
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Mixed Numeric Expressions

• 2 4.0
• 6 - 4.0
• 6 3.0
• 6 / 3.0
• 6 3.0
• 6 // 3.0
• -5.0
• 32.0

03-06.py
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Relational operators relate two operands

• 7 gt 10
• 4 lt 16
• 4 4
• 4 lt 4
• 4 gt 4
• 4 ! 4
• 4 ltgt 4

The result of these expressions is either true
or false (Boolean).
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Boolean expressions result in values true or false

• 7 gt 10
• 4 lt 16
• 4 4
• 4 lt 4
• 4 gt 4
• 4 ! 4
• 4 ltgt 4

03-07.py
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PythonData Types and Processing

• 3.1 Data types
• 3.2 Number processing
• 3.3 String Processing
• 3.4 Converting one type to another

26
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. 3.142e-10, 98.6)
• string (text, e.g. "Anne", 'Anne', "Hello
  World!")

There are other data types (e.g. lists,
dictionaries, files) which will be introduced
later in the course.
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String Objects
03-08.py

• string text, e.g.
• "Anne"
• 'Anne'
• "where's the
  spam?"

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String Assignments

• a "Hello out there"
• print a
• b 'Hello'
• print b
• c "Where's the spam?"
• print c
• d 'x'
• print d

03-09.py
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String Concatenation (joining)

• a 'Hello out there'
• b "Where's the spam?"
• c a b
• print c

03-10.py
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PythonData Types and Processing

• 3.1 Data types
• 3.2 Number processing
• 3.3 String Processing
• 3.4 Converting one type to another

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Converting one data type to another (int to str)

• 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

03-11.py
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Converting one data type to another (str to int)

• a "10"
• b '99'
• c a b
• print c
• print type(c)
• c int(c)
• print c
• print type(c)

03-12.py
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Rounding a floating point number to the nearest
integer

• 03-13.py
• How to round up a floating point number
• to the nearest integer
• x 1.6
• print x
• x round(x)
• print x
• x int(x)
• print x

03-13.py
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This presentation uses the following program
files

• http//www.annedawson.net/PythonPrograms.txt
• 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

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End of Python_Data_Types.ppt
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• Last updated Thursday 23rd October 2008, 926
  PT, AHD