Python

Python

1. Interactive interface vs writing scripts

   • Interactive interface
     • Is when You type directly to python one line at a time and it responds
       • Example:
         • x=2 print x y=x+2 print y
   • Writing scripts
     • Is when you enter a sequence of statements (lines) into a file using a text editor
       • Python execute the statements in the file
         • csev$ cat hello.py print 'Hello world!' csev$ python hello.py Hello world! csev$
         • Example:
   • Program steps
     • Conditional
       • Are steps that may be skipped
         • Example:
           • X=5 If x<10 Print “smaller” If x>20 Print “bigger” Print “finish”
     • Repeated
       • Have interaction variables that change each time through a loop
         • Example:
           • N=5 While n>0: Print n N=n-1 Print “blastoff”
     • Store
       • Are a set of steps to be used over and over as needed several places throughout the program
         • Example:
           • y=5 print y z=y-3 print z

2. Reserverd words

   • Is the python vocabulary
     • They have one and only meaning to Python
       • Are different from the variables
       • The principal reserved words are:
         • And, from, not, while, as, elif, global, or, with, assert, else, if, pass, yield, break, except, import, print, class, exec, in, raise, continue, finally, is, return, def, for, lambda, try.
       • Example
         • When we train a dog, if you say, “I wish more people would walk to improve their overall health”, what most dogs likely hear is, “blah blah blah walk blah blah blah blah”; because walk is it reserved word.

3. Types of errors

   • Syntax error
     • Is when you have violated the “grammar” rules of Python.
   • Logic errors
     • Is when your program has good syntax but there is a mistake in the order of the statements or perhaps a mistake in how the statements relate to one another.
       • Example:
         • Take a drink from your water bottle, put it in your backpack, walk to the library, and then put the top back on the bottle.
   • Semantic errors
     • Is when your description of the steps to take is syntactically perfect and in the right order, but there is simply a mistake in the program
       • It means that:
         • The program is perfectly correct but it does not do what you intended for it to do