chapter 1

Question 1

Code compilation

Answer 1

source code -> byte code and byte code is platform independent

Question 2

what does a byte code look like

Answer 2

*.pyc

sometimes, the *.pyc cannot be written into your system, but the script is still be run

Question 3

PVM

The last step of what is called the Python interpreter

Answer 3

python virtual machine that iterates through your byte code instructions one by one.

Question 4

exit an interactive python session

Answer 4

ctrl + D

Question 5

When do we have to use print

Answer 5

in the text file, we have to use print to show the result

in the interactive window, we don’t need to

Question 6

route the output of a Python script to a file to save it for later use

Answer 6

python filename.py > filename

Question 7

import script

Answer 7

> > > import script

Question 8

top-level file

Answer 8

one which launches the entire program

Question 9

what will import do

Answer 9

find the files->compile them to byte code->run the code

So import is an expensive operation

Question 10

How to reload the same module

Answer 10

reload(module name)

Question 11

what is the difference between a reload and an import

Answer 11

reload must have a parenthesis and import don’t

Question 12

Mostly, what is a module

Answer 12

More generally, a module is mostly just a package of variable names, known as a namespace

Question 13

how to use the content in the module

Answer 13

First, the module must be imported. Second, the attribute in the file should be used with prefix which is the name of the file

Question 14

How to import a specific attribute from a module

Answer 14

from module_name import attribute name

In this case, the use of the attribute is direct and no prefix is needed to specified in the command

Question 15

What is the difference between from filename import attributes
and import wholemodule

Answer 15

The import command executes the module and from ~~ copy the attribute names. That is why in the second case, the prefix is not needed

Question 16

How to show the available attributes in the module we defined

Answer 16

dir(module_name)

Question 17

What is the largest program structure in python?

Answer 17

module

Question 18

modules and namespace

Answer 18

the variables in one module is self-contained and independent of other modules. It cannot see other attributes in other modules except it imports other file explicitly.

Question 19

The characteristics of running a module using execfile(‘module.py’)

Answer 19

every time we use execfile to run a module, the module is runs anew

Question 20

which environmental variable specifies the searching path of modules

Answer 20

PYTHONPATH which initialize the sys.path attribute

Question 21

When you run a module, you have to reload the nested moduels

Answer 21

Because if you have import the nested module before, you may need to reload the module again if you run the module which nests other modules

Question 22

Dynamically typed

Answer 22

Python tracks the types automatically for us. We don’t need to declare the types explicitly for variables

Question 23

What is the difference between the expression
3.14152
and
print 3.14152

Answer 23

The result of the first one is 6.283000000000…4 which is not user friendly
the result of the second one is 6.283 which is user friendly

Question 24

how to represent string

Answer 24

single quote and double quote work the same

Question 25

check the length of a tring

Answer 25

len(‘string’) which is a built-in command

Question 26

ways to access a string

and the interesting way

Answer 26

s='Spam'
s[0]='S'
s[1]='p'
interesting way:
s[-1]: the last item in S
We should notice that s[len(S)-1] is the last character in the string

Question 27

A Gotcha

Answer 27

S[1:3} gives the content ‘pa’ if S is ‘Spam’ which doesn’t include m.

Question 28

fortran style access to a string

Answer 28

S[1:] 'pam'
S[0:3} 'Spa'
S[:3] 'Spa'
***S[:-1] 'Spa'
S[:] 'Spam'

Question 29

string concatenation

Answer 29

operator is + like C++
S+'xyz'     'Spamxyz'
operator *
S*8
'SpamSpam~~~~~Spam'

Question 30

Immutability of a string

Answer 30

A string cannot be changed in python once they are created

So in order to ‘change’ it, we just create a new one with the same name

Question 31

Is a tuple mutable?

Answer 31

No, it is not.

Question 32

substring search operation

Answer 32

stringname.find(‘substring’)

Question 33

Replace occurrences of a substring with another

Answer 33

stringname.replace(‘substring’,substitute’)

Question 34

is Python case sensitive?

Answer 34

Yes, Python is case sensitive

Question 35

Split a string into substrings on a delimiter

Answer 35

stringname.split(‘delimiter’)

Question 36

see the callable command for a string

Answer 36

dir(stringname) shows all the callable command

help(stringname.command) gives the command detailed help

Question 37

how to check the binary value of a string

Answer 37

ord(‘string_name’)