(00) How to run python?

> python
Python 2.4.3 (#1, Aug  2 2006, 22:24:22) 
[GCC 3.3.4] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 



(01) Let's do the followings:

>>> 1 + 5
6
>>> 2 * 5
10
>>> 1 / 2
0
>>>



(02) Is it the right answer?
    Then, do the followings:

>>> float(1 / 2)
0.0
>>> 1 / 2.0
0.5
>>> float(1)/2
0.5
>>> 1 / float(2)
0.5
>>>



(03) How about these?

>>> 'aaa'
'aaa'
>>> len('aaa')
3
>>>




(04) What happened?
    Read carefully the error message (if you have), and explain it.

>>> len('aaa') + len('bbb')
6
>>> len('aaa') + len('bbb') + 4
10
>>> 'aaa' + 'bbb'
'aaabbb'
>>> 'aaa' + 5
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: cannot concatenate 'str' and 'int' objects
>>>



(05) How to protect you from this kind of problem?

>>> type(1)
<type 'int'>
>>> type('1')
<type 'str'>
>>> type(1.0)
<type 'float'>
>>>



(06) You can associate a name to a value:

>>> a = 10 
>>> a
10
>>>



(07) The interpreter displays the value (10) of the variable (a).
    Read carefully the error message (if you have), and explain it.

>>> myVar = 'one sentence'
>>> myVar
'one sentence'
>>> 1string = 'one string'
  File "<stdin>", line 1
      1string = 'one string'
            ^
SyntaxError: invalid syntax
>>>
>>> myvar
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
NameError: name 'myvar' is not defined
>>>



(08) What appended?

>>> a = 2
>>> a
2
>>> a * 5
10
>>> b = a * 5
>>> b
10
>>> a = 1
>>> b
10
>>>



(09) Why hasn't b changed?
     What is the difference between the followings:

>>> b = a * 5
>>>
>>> b = 5
>>>



(10) What is the differerence between the followings:
     What do you conclude about the type of a variable?

>>> a = 1     #in this case a is a number
>>> a + 2
3
>>> a = '1'   #in this case a is a string
>>> a + 1
 Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: cannot concatenate 'str' and 'int' objects 
>>>



(11) The following will be explained later:

>>> from string import * 
>>>



(12) Can we perform calculus on strings?

>>> myString='abc'
>>> myString * 3
'abcabcabc'
>>> myString1 = 'abcdefghijklmnopqr'
>>> myString2 = 'ggghhhiiijjjkkklll'
>>>



(13) How do you concatenate myString1 and myString2 in a single string?

>>> myString = myString1 + myString2
'abcdefghijklmnopqrggghhhiiijjjkkklll'
>>>



(14) What is the length of the string myString?

>>> len(myString)
36
>>


(15) Does the string myString contain the character 'c'?

>>>  'c' in myString
True
>>>


(16) Does it contain 'm'?

>>> 'm' in myString
False
>>>



(17) Do the followings:
     And explain why.
 
>>> myString[0]
'a'   
>>> myString[1]
'b'  



(18) Display the 10th character.

>>> myString[9]
'j'


(19) Find the index of the last character.

>>> len(myString)
36
>>> myString[35]
'l'
>>>



(20) Find a more generic way to do it.

>>> myString[len(myString) - 1] 
'l'



(21) Python provides a special form to get the characters from the end of a string:

>>> myString1[-1]
'r'
>>> myString1[-4]
'o'
>>>


(22) Do the following, then what do you get?

>>> myString1[0] + myString1[5] + myString1[10]
'afk'
>>>



(23) Python provides a form to get 'slices' from strings:
>>> myString[0:3]
'abc'
>>> myString[3:6]
'def'



(24) How many of each character does this string contain?

>>> count(myString, 'a')
1
>>> count(myString, 'c')
1
>>> count(myString, 'k')
4
>>> count(myString, 'l')
r
>>>



(25) Count the percentage of 'k' on the string myString.

>>> totalCount = len(myString)
>>> localCount = count(myString, 'k')
>>> percentage = (localCount / totalCount) * 100
>>> percentage
>>> 0


(26) What happened?
     Can you correct this?

>>> float(localCount) / totalCount * 100    



(27) How to find specific pattern on a string:
     Do the following and explain why?

>>> myString = """abcdefghijklmnopqrstuvwxyz
zyxwvutsrqponmlkjihgfedcba"""
>>> myString1 = 'ABCDEF'
>>> myString2 = 'FEDCAB' 
>>> count(myString, myString1)
0
>>>
>>> 'abcdef' == 'abcdef'
True
>>> 'abcedf' == 'ABCDEF'
False
>>>



(28) How to change the case of a string?

>>> myString11 = lower(myString1)
>>> myString11
'abcdef'
>>> count(myString, myString11)
1
>>>



(29) Display the string myString.
     Do you see a character that you don't expect to have in myString?
     Then, how to remove it?
     
>>> myString
'abcdefghijklmnopqrstuvwxyz\nzyxwvutsrqponmlkjihgfedcba'
>>> len(myString)
>>> 53
>>> myString = replace(myString, '\n', '')
>>> myString
'abcdefghijklmnopqrstuvwxyzzyxwvutsrqponmlkjihgfedcba'
>>> len(myString)
>>> 52



(30) How to exit Python shell?
>>> ^D