Using stings And numbers in Python

Starting codeEditor
  Depending on your operating system, you will start codeEditor in different ways.
  Once it is installed on your system with Python, on Linux or Unix-based systems, you can just type python in a terminal or shell window and it will start.

Using string in python 

>>> “This text really won’t do anything”
“This text really won’t do anything”
>>> ‘This is also a string’
‘This is also a string’
>>> “””This is a third string that is some
   ...      how different”””
‘This is a third string that is some\n     how different’
>>> ‘And he said \’this string has escaped quotes\’’
“And he said ‘this string has escaped quotes’”

//Using + to Combine Strings
>>> “John” + “Q.” + “Public”
‘JohnQ.Public’
>>> “John” + “ “ + “Q.” + “ “ + “Public”
‘John Q. Public’
//Using a Format Specifier to Populate a String
//In the simplest case, you can do the same thing with your friend, John Q.:
>>> “John Q. %s” % (“Public”)
    ‘John Q. Public’
//More String Formatting
//You can do a couple of useful things when formatting a simple string:
>>> “%s %s %10s” % (“John”, “Q.”, “Public”)
   ‘John Q.        Public’
>>> “%-10s %s %10s” % (“John”, “Q.”, “Public”)
   ‘John         Q.       Public’

Numbers in Python
Python offers four different kinds of numbers with which you can work: integers, long numbers
 (or longs), floating-point numbers (or floats), and imaginary numbers.

>>> type(1)
<type ‘int’>
>>> type(2000)
<type ‘int’>
>>> type(999999999999)
<type ‘long’>
>>> type(1.0)
<type ‘float’>

Creating an Imaginary Number

The imaginary number behaves very much like a float, except that it cannot be mixed with a float. When

you see an imaginary number, it will have the letter j trailing it:

    >>> 12j

    12j

You can combine imaginary and nonimaginary numbers to create complex numbers:

   >>> 12j + 1

   (1+12j)

   >>> 12j + 1.01

   (1.01+12j)

   >>> type (12j + 1)

   <type ‘complex’>

Including Different Numbers in Strings

When you combined two strings in the first chapter by using a format specifier, you used the format

specifier %s, which means “a string.” Because numbers and strings have different types, you will use a

different specifier that will enable your numbers to be included in a string:

     >>> “Including an integer works with %%d like this: %d” % 10

     ‘Including an integer works with %d like this: 10’

     >>> “An integer converted to a float with %%f: %f” % 5

     ‘An integer converted to a float with %f: 5.000000’

     >>> “A normal float with %%f: %f” % 1.2345

     ‘A normal float with %f: 1.234500’

     >>> “A really large number with %%E: %E” % 6.789E10

     ‘A really large number with %E: 6.789000E+10’

     >>> “Controlling the number of decimal places shown: %.02f” % 25.101010101

     ‘Controlling the number of decimal places shown: 25.10’

  Escaping the % Sign in Strings

One other trick was shown before. In case you wanted to print the literal string %d in your program, you

achieve that in Python strings by using two % signs together. This is needed only when you also have

valid format specifiers that you want Python to substitute for you in the same string:

    print “The %% behaves differently when combined with other letters, like this: %%d

    %%s %%f %d” % 10

    The % behaves differently when combined with other letters, like this: %d %s %f 10

Doing Basic Math

You can enter basic arithmetic at the Python shell prompt and use it like a calculator. Like a calculator,

Python will accept a set of operations, and when you hit the Enter key, it will evaluate everything you’ve

typed and give you your answer:

    >>> 5 + 300

    305

    >>> 399 + 3020 + 1 + 3456

    6876

    >>> 300 - 59994 + 20

    -59674

    >>> 4023 - 22.46

    4000.54

>>> 2000403030 * 392381727

784921595607432810L

>>> 2000403030 * 3923817273929

7849215963933911604870L

>>> 2e304 * 3923817273929

inf

>>> 2e34 * 3923817273929

7.8476345478579995e+46

>>> 44 / 11

4

>>> 324 / 101

3

>>> 324.0 / 101.0

3.2079207920792081

>>> 324.0 / 101

3.2079207920792081

>>> 5 % 3

2

Printing the Results

Try actually printing the results, so that the preceding math with the unusual-looking results has its

results displayed to a user, as it would from inside of a program:

    >>> print “%f” % (4023 - 22.4)

    4000.600000

Using Math Operations

When you’re thinking about a particular set of mathematical operations, it can seem straightforward

when you write it down (or type it in). When you look at it later, however, it can become confusing. Try

these examples, and imagine them without the parentheses:

    >>> (24 * 8)

    192

    >>> (24 * (8 + 3))

    264

    >>> (24 * (8 + 3 + 7.0))

    432.0

   

Using Number Formats

Try this, for example. Here, you print a number as though you were printing a dollar amount:

    >>> print “$%.02f” % 30.0

    $30.00