variable_types

=Variable Types=

Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory. Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals, or characters in these variables. = Assigning Values to Variables: = Python variables do not have to be explicitly declared to reserve memory space. The declaration happens automatically when you assign a value to a variable. The equal sign (=) is used to assign values to variables. The operand to the left of the = operator is the name of the variable, and the operand to the right of the = operator is the value stored in the variable. For example: code #!/usr/bin/python

counter = 100         # An integer assignment miles  = 1000.0       # A floating point name   = "John"       # A string

print counter print miles print name code || Here 100, 1000.0 and "John" are the values assigned to //counter//, //miles// and //name// variables, respectively. While running this program, this will produce following result: code 100 1000.0 John code || = Multiple Assignment: = You can also assign a single value to several variables simultaneously. For example: code a = b = c = 1 code || Here, an integer object is created with the value 1, and all three variables are assigned to the same memory location. You can also assign multiple objects to multiple variables. For example: code a, b, c = 1, 2, "john" code || Here two integer objects with values 1 and 2 are assigned to variables a and b, and one string object with the value "john" is assigned to the variable c. = Standard Data Types: = The data stored in memory can be of many types. For example, a person.s age is stored as a numeric value and his or her address is stored as alphanumeric characters. Python has some standard types that are used to define the operations possible on them and the storage method for each of them. Python has five standard data types: > > > > > = Python Numbers: = Number data types store numeric values. They are immutable data types, which means that changing the value of a number data type results in a newly allocated object. <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Number objects are created when you assign a value to them. For example: code <span style="font-family: 'Courier New',monospace; font-size: 12px;">var1 = 1 var2 = 10 code || <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">You can also delete the reference to a number object by using the **del** statement. The syntax of the del statement is: code <span style="font-family: 'Courier New',monospace; font-size: 12px;">del var1[,var2[,var3[....,varN]]]] code || <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">You can delete a single object or multiple objects by using the del statement. For example: code <span style="font-family: 'Courier New',monospace; font-size: 12px;">del var del var_a, var_b code || <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Python supports four different numerical types: > > > >
 * <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: left;"> Numbers
 * <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: left;"> String
 * <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: left;"> List
 * <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: left;"> Tuple
 * <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: left;"> Dictionary
 * <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: left;"> int (signed integers)
 * <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: left;"> long (long integers [can also be represented in octal and hexadecimal])
 * <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: left;"> float (floating point real values)
 * <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: left;"> complex (complex numbers)

Examples:
<span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Here are some examples of numbers: > > = Python Strings: = <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Strings in Python are identified as a contiguous set of characters in between quotation marks. <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Python allows for either pairs of single or double quotes. Subsets of strings can be taken using the slice operator ( [ ] and [ : ] ) with indexes starting at 0 in the beginning of the string and working their way from -1 at the end. <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">The plus ( + ) sign is the string concatenation operator, and the asterisk ( * ) is the repetition operator.
 * ~ int ||~ long ||~ float ||~ complex ||
 * 10 || 51924361L || 0.0 || 3.14j ||
 * 100 || -0x19323L || 15.20 || 45.j ||
 * -786 || 0122L || -21.9 || 9.322e-36j ||
 * 080 || 0xDEFABCECBDAECBFBAEl || 32.3+e18 || .876j ||
 * -0490 || 535633629843L || -90. || -.6545+0J ||
 * -0x260 || -052318172735L || -32.54e100 || 3e+26J ||
 * 0x69 || -4721885298529L || 70.2-E12 || 4.53e-7j ||
 * <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: left;"> Python allows you to use a lowercase L with long, but it is recommended that you use only an uppercase L to avoid confusion with the number 1. Python displays long integers with an uppercase L.
 * <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: left;"> A complex number consists of an ordered pair of real floatingpoint numbers denoted by a + bj, where a is the real part and b is the imaginary part of the complex number.

Example:
code <span style="font-family: 'Courier New',monospace; font-size: 12px;">#!/usr/bin/python

str = 'Hello World!'

print str         # Prints complete string print str[0]      # Prints first character of the string print str[2:5]    # Prints characters starting from 3rd to 6th print str[2:]     # Prints string starting from 3rd character print str * 2     # Prints string two times print str + "TEST" # Prints concatenated string code || <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">This will produce following result: code <span style="font-family: 'Courier New',monospace; font-size: 12px;">Hello World! H llo llo World! Hello World!Hello World! Hello World!TEST code || = Python Lists: = <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Lists are the most versatile of Python's compound data types. A list contains items separated by commas and enclosed within square brackets ([]). <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">To some extent, lists are similar to arrays in C. One difference between them is that all the items belonging to a list can be of different data type. <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">The values stored in a list can be accessed using the slice operator ( [ ] and [ : ] ) with indexes starting at 0 in the beginning of the list and working their way to end-1. <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">The plus ( + ) sign is the list concatenation operator, and the asterisk ( * ) is the repetition operator.

Example:
code <span style="font-family: 'Courier New',monospace; font-size: 12px;">#!/usr/bin/python

list = [ 'abcd', 786, 2.23, 'john', 70.2 ] tinylist = [123, 'john']

print list         # Prints complete list print list[0]      # Prints first element of the list print list[1:3]    # Prints elements starting from 2nd till 3rd print list[2:]     # Prints elements starting from 3rd element print tinylist * 2 # Prints list two times print list + tinylist # Prints concatenated lists code || <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">This will produce following result: code <span style="font-family: 'Courier New',monospace; font-size: 12px;">['abcd', 786, 2.23, 'john', 70.200000000000003] abcd [786, 2.23] [2.23, 'john', 70.200000000000003] [123, 'john', 123, 'john'] ['abcd', 786, 2.23, 'john', 70.200000000000003, 123, 'john'] code || = Python Tuples: = <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">A tuple is another sequence data type that is similar to the list. A tuple consists of a number of values separated by commas. Unlike lists, however, tuples are enclosed within parentheses. <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">The main differences between lists and tuples are: Lists are enclosed in brackets ( [ ] ), and their elements and size can be changed, while tuples are enclosed in parentheses and cannot be updated. Tuples can be thought of as **read-only** lists.

Example:
code <span style="font-family: 'Courier New',monospace; font-size: 12px;">#!/usr/bin/python

tuple = ( 'abcd', 786, 2.23, 'john', 70.2 ) tinytuple = (123, 'john')

print tuple          # Prints complete list print tuple[0]       # Prints first element of the list print tuple[1:3]     # Prints elements starting from 2nd till 3rd print tuple[2:]      # Prints elements starting from 3rd element print tinytuple * 2  # Prints list two times print tuple + tinytuple # Prints concatenated lists code || <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">This will produce following result: code <span style="font-family: 'Courier New',monospace; font-size: 12px;">('abcd', 786, 2.23, 'john', 70.200000000000003) abcd (786, 2.23) (2.23, 'john', 70.200000000000003) (123, 'john', 123, 'john') ('abcd', 786, 2.23, 'john', 70.200000000000003, 123, 'john') code || <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Following is invalid with tuple, because we attempted to update a tuple,which is not allowed. Similar case is possible with lists: code <span style="font-family: 'Courier New',monospace; font-size: 12px;">#!/usr/bin/python

tuple = ( 'abcd', 786, 2.23, 'john', 70.2 ) list = [ 'abcd', 786, 2.23, 'john', 70.2 ] tuple[2] = 1000   # Invalid syntax with tuple list[2] = 1000    # Valid syntax with list code || = Python Dictionary: = <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Python 's dictionaries are hash table type. They work like associative arrays or hashes found in Perl and consist of key-value pairs. <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Keys can be almost any Python type, but are usually numbers or strings. Values, on the other hand, can be any arbitrary Python object. <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Dictionaries are enclosed by curly braces ( { } ) and values can be assigned and accessed using square braces ( [] ).

Example:
code <span style="font-family: 'Courier New',monospace; font-size: 12px;">#!/usr/bin/python

dict = {} dict['one'] = "This is one" dict[2]    = "This is two"

tinydict = {'name': 'john','code':6734, 'dept': 'sales'}

print dict['one']      # Prints value for 'one' key print dict[2]          # Prints value for 2 key print tinydict         # Prints complete dictionary print tinydict.keys  # Prints all the keys print tinydict.values # Prints all the values code || <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">This will produce following result: code <span style="font-family: 'Courier New',monospace; font-size: 12px;">This is one This is two {'dept': 'sales', 'code': 6734, 'name': 'john'} ['dept', 'code', 'name'] ['sales', 6734, 'john'] code || <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Dictionaries have no concept of order among elements. It is incorrect to say that the elements are "out of order"; they are simply unordered. = Data Type Conversion: = <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">Sometimes you may beed to perform conversions between the built-in types. To convert between types you simply use the type name as a function. <span style="background-color: #ffffff; font-family: verdana,helvetica,arial,sans-serif; font-size: 11px; text-align: justify;">There are several built-in functions to perform conversion from one data type to another. These functions return a new object representing the converted value.
 * ~ Function ||~ Description ||
 * int(x [,base]) || Converts x to an integer. base specifies the base if x is a string. ||
 * long(x [,base] ) || Converts x to a long integer. base specifies the base if x is a string. ||
 * float(x) || Converts x to a floating-point number. ||
 * complex(real [,imag]) || Creates a complex number. ||
 * str(x) || Converts object x to a string representation. ||
 * repr(x) || Converts object x to an expression string. ||
 * eval(str) || Evaluates a string and returns an object. ||
 * tuple(s) || Converts s to a tuple. ||
 * list(s) || Converts s to a list. ||
 * set(s) || Converts s to a set. ||
 * dict(d) || Creates a dictionary. d must be a sequence of (key,value) tuples. ||
 * frozenset(s) || Converts s to a frozen set. ||
 * chr(x) || Converts an integer to a character. ||
 * unichr(x) || Converts an integer to a Unicode character. ||
 * ord(x) || Converts a single character to its integer value. ||
 * hex(x) || Converts an integer to a hexadecimal string. ||
 * oct(x) || Converts an integer to an octal string. ||