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CS204- Homework 4 Solved

Introduction

 In this homework, you are asked to implement a program which analyzes whether a given .py file (python source code) contains indentation errors. Hence, you must check if each line can be bounded by an indentation level correctly. To achieve this, the program must use a

stack data structure. The details of the methods, algorithms and the data structure to be used will be given in the subsequent sections of this homework specification.

 

Program Flow, Input and Output

At first, the program asks for the name of the .py file to be analyzed. You should check whether the file has been opened successfully or not. In case of a file open failure, ask for a different file name until it is opened successfully. While reading the content of the .py file, your program is going to print the content information and indentation correctness for each line. As soon as a syntax error related to indentation is detected, your program will display an error message and will stop without checking the rest of the file. If all of the lines are checked correctly, then a general success message will be displayed at the end. 

 

In Python language, code blocks are grouped according to their indentation levels, instead of using symbols like { and }, which are used to identify blocks in C++. Thus, there are specific rules for indentation in Python.

 

            Indentation Rules to be Checked by Your Program and Other Assumptions:

1.     Initial indentation level has depth zero (i.e. there must not be any leading blanks to start with).

2.     Code lines belonging to the same indentation level (i.e. the code lines of the same block) must have the same number of spaces at the beginning of the lines.

3.     The lines proceeding a keyword-containing line (keywords are explained below) must start a new indentation level. This new level is going to have a greater depth than the previous level. As long as the new level has more spaces than the previous one, new level depth is going to be valid.

4.     A keyword-containing line is defined as a line that starts with a keyword (after some blanks, if any). You are responsible for checking 5 keywords, which are if, else, elif, for and while. 

a. You are not required to check the syntax related to the correctness of the order of these keywords. For example, your program will not check whether an else or elif has a preceding if.

5.     It is possible to have nested blocks. That means, before ending a block, a new block may start. This way, nested indentation levels may be created. 

6.     When a block is finished, a python code may continue with one of the outer blocks (i.e. one of the previous indentation levels; one or more previous levels can be gone back in one line). 

7.     You are not going to check for Python syntax errors other than indentation errors. For instance, checking for incomplete assignment (x =),  etc. is not in the scope of this homework (we are not going to create a compiler J).

8.     You can assume that the input file does not contain any comments and does not contain any empty lines. 

9.     You can assume that no tab characters are used in .py files. Indentation level depths are counted by the number of leading spaces (blank characters) at the beginning of the lines. 

 

Data Structure to be Used

In this homework you are going to use STACKS ONLY. It is used to keep track of the indentation level depth of the input .py file. The stack class that we provide together with the lecture notes, DynIntStack.cpp and DynIntStack.h, must be used in your program and they must not be modified. Your main program must be written as another cpp file.

 

You should delete all of the remaining nodes in the stack before finishing the program.

 

You cannot use any other multiple data container (vector, built-in array, dynamic array, other linked lists, etc.) in this homework.

 

Algorithmic Hint

 You will only need a single stack to keep track of the indentation levels. At first, push the initial indentation level, which is 0, to the stack. Then,

 

process the input file line by line.  

if the current line contains more leading spaces than the current indentation level and a KEYWORD is observed just BEFORE this line.

the line is correctly indented with a new indentation level. Push the new indentation level (number of leading spaces of the current line) to the stack. 

else if a KEYWORD is observed just BEFORE this line, but the amount of spaces at the beginning of this line is less than or same as the current indentation level,  this is an error case. 

else if NO KEYWORD is observed just BEFORE this line and the current indentation level has more spaces than the current line's number of leading spaces,  pop the current indentation level(s) from the stack until a correct block is found. If a correct level cannot be found, then this is an error.

else if NO KEYWORD is observed just BEFORE this line and the current indentation level has less spaces than the current line's number of leading spaces,  this is an error case.

else if NO KEYWORD is observed just BEFORE this line and the current indentation level has the same amount spaces as the current line's number of leading spaces,  the line is correctly indented and belongs to current indentation level.

 

Sample Runs

Some sample runs are given below, but these are not comprehensive, therefore you have to consider all possible cases to get full mark. The sample input files are provided in the .zip package of this homework.

 

 

Sample Run 1:

File: t1.py

import sys  import random              ans = True     while ans:     

     question = raw_input("Ask the magic 8 ball a question: (press enter to quit) ")      answers = random.randint(1,8)      if question == "":

                sys.exit()      elif answers == 1:

                print "It is certain"      elif answers == 2:

                print "Outlook good"      elif answers == 3:

                                                           print "You may rely on it"      elif answers == 4:

                print "Ask again later"      elif answers == 5:                  print "Concentrate and ask again"

 

    elif answers == 6:

 

          print "Reply hazy, try again"

 

    elif answers == 7:

 

                        print "My reply is no"

 

     elif answers == 8:

                print "My sources say no" print "End"  
 

 

Please enter the file name that is going to be analyzed.

t1.py

Starting file analysis...

Initial indentation level is pushed to the stack as 0.

 

Line number: 1

Line: import sys

0 number of spaces observed before the start of the line. Current Level = 0 This Line = 0 Line belongs to current block.

 

Line number: 2

Line: import random

0 number of spaces observed before the start of the line. Current Level = 0 This Line = 0 Line belongs to current block.

 

Line number: 3

Line: ans = True

0 number of spaces observed before the start of the line.

Current Level = 0 This Line = 0

Line belongs to current block.

 

Line number: 4

Line: while ans:

0 number of spaces observed before the start of the line. Current Level = 0 This Line = 0 Line belongs to current block.

Keyword while found on this line.

 

Line number: 5

Line:     question = raw_input("Ask the magic 8 ball a question: (press enter to quit) ") 4 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 0 This Line = 4

Line correct. Depth 4 added to the stack.

 

Line number: 6

Line:     answers = random.randint(1,8)

4 number of spaces observed before the start of the line. Current Level = 4 This Line = 4 Line belongs to current block.

 

Line number: 7

Line:     if question == "":

4 number of spaces observed before the start of the line. Current Level = 4 This Line = 4 Line belongs to current block.

Keyword if found on this line.

 

Line number: 8

Line:         sys.exit()

8 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 4 This Line = 8

Line correct. Depth 8 added to the stack.

 

Line number: 9

Line:     elif answers == 1:
4 number of spaces observed before the start of the line.

Current Level = 8 This Line = 4
Current line is smaller than Current indentation level; checking if line belongs to outer indentation.
Current Level = 4 This Line = 4

Line belongs to outer block. Keyword elif found on this line.
 

Line number: 10
Line:         print "It is certain"

8 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 4 This Line = 8

Line correct. Depth 8 added to the stack.

 

Line number: 11

Line:     elif answers == 2:

4 number of spaces observed before the start of the line.

Current Level = 8 This Line = 4

Current line is smaller than Current indentation level; checking if line belongs to outer indentation.

Current Level = 4 This Line = 4

Line belongs to outer block.

Keyword elif found on this line.

 

Line number: 12

Line:         print "Outlook good"

8 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 4 This Line = 8

Line correct. Depth 8 added to the stack.

 

Line number: 13

Line:     elif answers == 3:                                                                                                                  

Current Level = 8 This Line =                                                                                                              4

Current line is smaller than Current indentation level; checking if line belongs to outer indentation. Current Level = 4 This Line =         4

Line belongs to outer block. Keyword elif found on this line.                                                                       

Line number:                                                                                                                                  14

 

4 number of spaces observed before the start of the line.

Line:                                                  print "You may rely on it" 49 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 4 This Line = 49

Line correct. Depth 49 added to the stack.

 

Line number: 15

Line:     elif answers == 4:

4 number of spaces observed before the start of the line.

Current Level = 49 This Line = 4

Current line is smaller than Current indentation level; checking if line belongs to outer indentation. Current Level = 4 This Line = 4 Line belongs to outer block.

Keyword elif found on this line.

 

Line number: 16

Line:         print "Ask again later"

8 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 4 This Line = 8

Line correct. Depth 8 added to the stack.

 

Line number: 17

Line:     elif answers == 5:

4 number of spaces observed before the start of the line.

Current Level = 8 This Line = 4

Current line is smaller than Current indentation level; checking if line belongs to outer indentation. Current Level = 4 This Line = 4

Line belongs to outer block.

Keyword elif found on this line.

 

Line number: 18

Line:                print "Concentrate and ask again" 15 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 4 This Line = 15

Line correct. Depth 15 added to the stack.

 

Line number: 19

Line:     elif answers == 6:

4 number of spaces observed before the start of the line.

Current Level = 15 This Line = 4

Current line is smaller than Current indentation level; checking if line belongs to outer indentation. Current Level = 4 This Line = 4 Line belongs to outer block.

Keyword elif found on this line.

 

Line number: 20

Line:           print "Reply hazy, try again"

10 number of spaces observed before the start of the line. This line proceeds a keyword containing line.

Current Level = 4 This Line = 10

Line correct. Depth 10 added to the stack.

 

Line number: 21

Line:     elif answers == 7:

4 number of spaces observed before the start of the line.

Current Level = 10 This Line = 4

Current line is smaller than Current indentation level; checking if line belongs to outer indentation. Current Level = 4 This Line = 4

Line belongs to outer block.

Keyword elif found on this line.

 

Line number: 22

Line:                         print "My reply is no"

24 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 4 This Line = 24

Line correct. Depth 24 added to the stack.

 

Line number: 23

Line:     elif answers == 8:

4 number of spaces observed before the start of the line.

Current Level = 24 This Line = 4

Current line is smaller than Current indentation level; checking if line belongs to outer indentation. Current Level = 4 This Line = 4 Line belongs to outer block.

Keyword elif found on this line.

 

Line number: 24

Line:         print "My sources say no"

8 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 4 This Line = 8

Line correct. Depth 8 added to the stack.

 

Line number: 25

Line: print "End"

0 number of spaces observed before the start of the line.

Current Level = 8 This Line = 0

Current line is smaller than Current indentation level; checking if line belongs to outer indentation.

Current Level = 4 This Line = 0

Current line is smaller than Current indentation level; checking if line belongs to outer indentation. Current Level = 0 This Line = 0 Line belongs to outer block.

 

Finished file analysis. File structure is correct!

Stack emptied and program ending.

 

Sample Run 2:

File: t2.py

 

   if error:print "wrong start"      

  print "error"
 

Please enter the file name that is going to be analyzed.

t2.txt

Unable to open file please enter a different file name. t2.cpp

Unable to open file please enter a different file name.

t2.py

Starting file analysis...

Initial indentation level is pushed to the stack as 0.

 

Line number: 1

Line:   print "wrong start"

2 number of spaces observed before the start of the line. Current Level = 0 This Line = 2

Incorrect file structure.

Current line cannot be greater than the Current indentation level. Stopping file analysis...

 

Stack emptied and program ending.

 

Sample Run 3:

File: t3.py

 

 line_start = 0  if line_start == 0

  elseline_start = 1      

        print "error"   print "here"
 

Please enter the file name that is going to be analyzed.

t3.py

Starting file analysis...

Initial indentation level is pushed to the stack as 0.

 

Line number: 1

Line: line_start = 0

0 number of spaces observed before the start of the line. Current Level = 0 This Line = 0 Line belongs to current block.

 

Line number: 2

Line: if line_start == 0

0                number of spaces observed before the start of the line. Current Level = 0 This Line = 0 Line belongs to current block.

Keyword if found on this line.

 

Line number: 3

Line:  line_start = 1

1                number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 0 This Line = 1

Line correct. Depth 1 added to the stack.

 

Line number: 4

Line: else

0 number of spaces observed before the start of the line.

Current Level = 1 This Line = 0

Current line is smaller than Current indentation level; checking if line belongs to outer indentation. Current Level = 0 This Line = 0 Line belongs to outer block.

Keyword else found on this line.

 

Line number: 5

Line:        print "error"

7 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 0 This Line = 7

Line correct. Depth 7 added to the stack.

 

Line number: 6

Line:  print "here"

1 number of spaces observed before the start of the line.

Current Level = 7 This Line = 1

Current line is smaller than Current indentation level; checking if line belongs to outer indentation.

Current Level = 0 This Line = 1

Incorrect file structure.

An indentation level same as the Current line is not found in outer blocks. Stopping file analysis...

 

Stack emptied and program ending.

 

 

Sample Run 4:

File: t4.py

 

x = 1        else  y = 0        if x == 1    

    x = 2

    if x == 2               print "here"    
 

 

Please enter the file name that is going to be analyzed. p4.py

Unable to open file please enter a different file name.

t4.py

Starting file analysis...

Initial indentation level is pushed to the stack as 0.

 

Line number: 1

Line: x = 1

0 number of spaces observed before the start of the line. Current Level = 0 This Line = 0 Line belongs to current block.

 

Line number: 2

Line: else

0 number of spaces observed before the start of the line. Current Level = 0 This Line = 0 Line belongs to current block.

Keyword else found on this line.

 

Line number: 3

Line: y = 0

0 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 0 This Line = 0

Incorrect file structure.

Current line must be greater than the Current indentation level. Stopping file analysis...

 

Stack emptied and program ending.

 

 

Sample Run 5:

File: t5.py

 

if True:          while True:            for x in range(1,20):    

                    else                           l =
Please enter the file name that is going to be analyzed.

t5.py

Starting file analysis...

Initial indentation level is pushed to the stack as 0.

 

Line number: 1 Line: if True:

0 number of spaces observed before the start of the line. Current Level = 0 This Line = 0 Line belongs to current block.

Keyword if found on this line.

 

Line number: 2

Line:      while True:

5 number of spaces observed before the start of the line.

This line proceeds a keyword containing line. Current Level = 0 This Line = 5

Line correct. Depth 5 added to the stack.

Keyword while found on this line.

 

Line number: 3

Line:           for x in range(1,20):

10 number of spaces observed before the start of the line.

This line proceeds a keyword containing line. Current Level = 5 This Line = 10

Line correct. Depth 10 added to the stack.

Keyword for found on this line.

 

Line number: 4

Line:                     else

20 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 10 This Line = 20

Line correct. Depth 20 added to the stack.

Keyword else found on this line.

 

Line number: 5

Line:                           l =

26 number of spaces observed before the start of the line.

This line proceeds a keyword containing line. Current Level = 20 This Line = 26 Line correct. Depth 26 added to the stack.

 

Finished file analysis. File structure is correct!

Stack emptied and program ending.

 

 

Sample Run 6:

File: t6.py

 

if True:          while True:            for x in range(1,20):                        if True:                           while True:                            else                                         l =  print "End"

 
 

Please enter the file name that is going to be analyzed.

t6.py

Starting file analysis...

Initial indentation level is pushed to the stack as 0.

 

Line number: 1

Line: if True:

0 number of spaces observed before the start of the line. Current Level = 0 This Line = 0 Line belongs to current block.

Keyword if found on this line.

 

Line number: 2

Line:      while True:

5 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 0 This Line = 5

Line correct. Depth 5 added to the stack.

Keyword while found on this line.

 

Line number: 3

Line:           for x in range(1,20):

10 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 5 This Line = 10

Line correct. Depth 10 added to the stack.

Keyword for found on this line.

 

Line number: 4

Line:                   if True:

18 number of spaces observed before the start of the line.

This line proceeds a keyword containing line. Current Level = 10 This Line = 18 Line correct. Depth 18 added to the stack.

Keyword if found on this line.

 

Line number: 5

Line:                       while True:

22 number of spaces observed before the start of the line.

This line proceeds a keyword containing line. Current Level = 18 This Line = 22

Line correct. Depth 22 added to the stack.

Keyword while found on this line.

 

Line number: 6

Line:                           else

26 number of spaces observed before the start of the line.

This line proceeds a keyword containing line. Current Level = 22 This Line = 26

Line correct. Depth 26 added to the stack.

Keyword else found on this line.

 

Line number: 7

Line:                                    l =

35 number of spaces observed before the start of the line.

This line proceeds a keyword containing line. Current Level = 26 This Line = 35

Line correct. Depth 35 added to the stack.

 

Line number: 8

Line: print "End"

0 number of spaces observed before the start of the line.

Current Level = 35 This Line = 0

Current line is smaller than Current indentation level; checking if line belongs to outer indentation.

Current Level = 26 This Line = 0

Current line is smaller than Current indentation level; checking if line belongs to outer indentation.

Current Level = 22 This Line = 0

Current line is smaller than Current indentation level; checking if line belongs to outer indentation.

Current Level = 18 This Line = 0

Current line is smaller than Current indentation level; checking if line belongs to outer indentation. Current Level = 10 This Line = 0

Current line is smaller than Current indentation level; checking if line belongs to outer indentation.

Current Level = 5 This Line = 0

Current line is smaller than Current indentation level; checking if line belongs to outer indentation. Current Level = 0 This Line = 0 Line belongs to outer block.

 

Finished file analysis. File structure is correct!

Stack emptied and program ending.

 

Sample Run 7:

File: t7.py

 

if True:          while True:            a = 78            for x in range(1,20):                    if x=1:  

 

           print "End"print "Muslera"                  

 
 

Please enter the file name that is going to be analyzed. t7.py

Starting file analysis...

Initial indentation level is pushed to the stack as 0.

 

Line number: 1 Line: if True:

0 number of spaces observed before the start of the line. Current Level = 0 This Line = 0 Line belongs to current block.

Keyword if found on this line.

 

Line number: 2

Line:      while True:

5 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 0 This Line = 5

Line correct. Depth 5 added to the stack.

Keyword while found on this line.

 

Line number: 3

Line:           a = 78

10 number of spaces observed before the start of the line.

This line proceeds a keyword containing line.

Current Level = 5 This Line = 10

Line correct. Depth 10 added to the stack.

 

Line number: 4

Line:           for x in range(1,20):

10 number of spaces observed before the start of the line. Current Level = 10 This Line = 10

Line belongs to current block.

Keyword for found on this line.

 

Line number: 5

Line:               if x=1:

14 number of spaces observed before the start of the line.

This line proceeds a keyword containing line. Current Level = 10 This Line = 14 Line correct. Depth 14 added to the stack. Keyword if found on this line.

 

Line number: 6

Line:           print "Muslera"

10 number of spaces observed before the start of the line.

This line proceeds a keyword containing line. Current Level = 14 This Line = 10

Incorrect file structure.

Current line must be greater than the Current indentation level. Stopping file analysis...

 

Stack emptied and program ending.

 

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