Python Introduction Workshop

Workshop

1.) Create a file

$ nano myprog.py

2.) Add the following line

print 'Hello World!'

3.) Save the file and exit. Ctrl+O, Ctrl+X

4.) Run the program.

$ python myprog.py

5.) Add a comment to the top of your program. Comments are to help people read your program.

# Program by [username]

6.) Create a variable to store input into the program.

# Import adds a library (addition functionality) to your program
# sys is the system library
import sys

# Read from stdin into a variable called instr
instr = sys.stdin.readline()

# Print message w/ variable
print 'Hello ' + instr + '.'

7.) Run the program, this time with input.

$ whoami | python myprog.py

8.) Use the input to alter the output, before your print message add:

if instr == 'jbg':
  instr = 'Programmer'
else:
  instr = 'Writer'

9.) Save and run.

10.) It doesn't work! This is because there is actually a return character in the string. Change the following:

instr = sys.stdin.readline().strip()

11.) Save and run.

$ whoami | python myprog.py
$ echo 'Ray Bradbury' | python myprog.py

12.) Create a new program (myprog2.py) which loops through all the lines coming from stdin.

 import sys

 for line in sys.stdin:
   print line

13.) Run it.

$ cat /pub/451.txt | python myprog2.py

14.) That's a lot of lines, how many exactly?

$ cat /pub/451.txt | python myprog2.py | wc -l

15.) Let's store those lines in an array.

import sys

lines = []
for line in sys.stdin:
  lines.append(line)

print 'Stored ' + str(len(lines)) + ' lines.'

What to talk about...

• Variables (integers, arrays)
• Conditionals (if/elif/else)
• Loops (for, while)
• Functions (def function_name(args):)

• Exception handling? (try/catch)
• File I/O...reading and writing from files:

f = open('handd-book.wiki', 'w') # write img_file = open(filename, 'wb') # i think append? f = open('handd-book.wiki', 'r') # read