1. Introduction to Python
Usman Roshan

2. Python
Interpreter language: the Python interpreter executes each statement one at a time.
No compilation or linking is required.
Python programs are called scripts which are simple text files. To execute a script we pass it through the interpreter.

3. Data types Basic data types Collections Integer Float String
Boolean (true or false)
Collections
Lists
Dictionaries (hash tables)
Sets
And more…

4. Expressions Numeric operators such as +, -, *, /, **
Logical operators such as and and or
String operators such as in, +, [], [:]
String and numeric functions such as len, abs, max, and min.

5. Assignment
name = value
Examples:
sequence = “ACCCATA”
x = 5
y = x + 2

6. Lists Ordered collection of basic types Examples: Operations on lists
Concatenate: list3 = list1 + list2
Access nth element: list1[n]

7. Dictionaries
Dictionaries are like arrays, except that they are indexed by user defined keys instead of non-negative integers.
Example
h={‘A’:’T’, ‘C’:’G’}
Operations on dictionaries
Lookup: h[key]

8. Input and Output
Input and output to files is done by creating a file object
open(path, mode)
Example:
f = open(“myfile.txt”,”r”)
f.readline()

9. Control structures Conditional statements if expression : statements1
else:
statements2
Example
max = 0
if(x > y):
max = x
max = y

10. Iteration for count in range(start,stop,step): for item in collection:
statements
for item in collection:
do something with item

11. Exercises Write a Python program to
Measure and print the average length of DNA sequences in a file
Determine the number of matches and mismatches between two DNA sequences of equal length
Read a matrix from a text file into a two dimensional array and determine the largest number in the matrix
Select random rows in a two dimensional array and print them to a file