1. Intro to CS Nov 17, 2016

2. Today Additional operations in list Additional operations in string
Dictionary

3. list data structure
A sequence of values. Order matters. Values can be any type. They are called elements or sometimes items.
empty_list = []
num_list = [17, 123]
mix_list = [34, 26, ‘abc’, 56, ‘xy’]
Use index to access data (positive or negative index)
[34, 26, ‘abc’, 56, ‘xy’]
| | | | |
index:
or :

4. access a list mix_list = [34, 26, ‘abc’, 56, ‘xy’]
access individual element with index
mix_list[2] = ‘abc’
mix_list[-2] = 56
In operator is for element search. Return True or False
if 26 in mix_list:
print(“find 26!!!”)
Traverse a list with For loop
for elem in mix_list:
elem = elem*2
print(elem, end=‘,’)

5. list slice syntax: list_name[start : stop : step]
example: txt=[11,22, 33,44,55,66,77]
txt[0:5]  start=0, stop= 5-1
txt[2:]  start=2, stop=end
txt[:3]  start=0, stop= 3-1
txt[0::2]  start=0, stop= end, step=2
txt[::]  print whole list

6. list execise myList = [‘a’, ‘b’, ‘c’, ’d’, ‘e’, ‘f’,’c’]
write down the result of these expressions
myList[3] =
myList[-3] =
myList[1:4] =
‘d’ in myList result is:
‘y’ in myList result is:

7. Lab 4.3.1 Write a python program that takes user input from stdin
Reverse the input string
Print the reversed string to stdout

8. Lab 4.3.1 solution inStr = input("Please enter your string: ")
newStr = ""
for idx in range(len(inStr) - 1, -1, -1):
newStr = newStr + inStr[idx]
print("Here is the reversed string: ", newStr)

9. Lab 4.3.1 solution 2 inStr = input("Please enter your string: ")
print("Solution 2: ", inStr[::-1])

10. [::-1] works for list myList = [1, 2, 3, 4]
print(”Reversed list: ", myList[::-1])

11. Separator in s.split myStr = 'Python*Is*Fun!'
myList = myStr.split(sep = "*")
print(myList)
>>>['Python', 'Is', 'Fun!']

12. Lab 4.3.2 Print the addresses using a for loop
adrList = ["Name = Bill Jones Address=123 Main Street" ,
"Name = Wm Smith Address=948 High Street" ,
"Name = Abe Lincoln Address=657 Gettysburg,DC",
"Name = Boss Hog Address=123 Deep South" ]

13. Lab 4.3.2 solution for item in adrList:
print (item.split("Address=")[1])

14. Dictionary
In Python, a “dictionary” is a data container that stores multiple items of data as a list of key:value pairs
The key:value pairs are unordered
Values are referenced by their associated keys
Key must be unique within a dictionary
Key is typically a string name

15. Dictionary Example Create a dictionary
>>>myDict ={'name':'Bob', 'ref':'Python', 'sys':'Win'}
>>>print(myDict)
{'ref': 'Python', 'sys': 'Win', 'name': 'Bob'}
Display a value referenced by its key
>>>Print(‘\nReference:’, myDict[‘ref’])
Reference: Python
Display all keys
>>>Print(‘\nKeys:’, myDict.keys())
Keys: dict_keys(['sys', 'name', 'ref'])

16. Dictionary Example Delete one pair from the dictionary
>>>del myDict['name']
Add a new pair
>>>myDict[‘user’] = ‘Tom’
Display the new dictionary
>>>print('Dictionary:', mydict)
Dictionary: {'sys': 'Win', 'ref': 'Python', 'user': 'Tom'}
Search a key
>>>print('Is there a name key?:', 'name' in myDict)
Is there a name key?: False

17. Sorted Keys() returns a list of keys in random order
Use sorted() to sort the keys
>>>sortedKeys = sorted(myDict.keys())
>>>print('\nsortedKeys:', sortedKeys)
sortedKeys: ['ref', 'sys', 'user']

18. Summary Additional operations in list Additional operations in string
Dictionary