python for everybody assignment 8.5

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8.5: List Slices

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The slice operator also works on lists:

If you omit the first index, the slice starts at the beginning. If you omit the second, the slice goes to the end. So if you omit both, the slice is a copy of the whole list.

Since lists are mutable, it is often useful to make a copy before performing operations that fold, spindle, or mutilate lists.

A slice operator on the left side of an assignment can update multiple elements:

Python Ex 8.5: in python4e

Hay , hope you are doing well,

it’s right answer for that quiz, but I feel that the quiz asked for a specific answer need help , and the line : if len(words) == 0 : continue can u tell me another way to do the same ?

link of quiz : https://www.py4e.com/tools/pythonauto/?PHPSESSID=f42fa792ce788dcae11b092ae158c67e

Well, the most similar to continue is pass However there are differences, continue transfers the control of the loop to the beginning. While pass is a definitive pass (ignore the failed loop) There is another commonly misunderstood, break is the contrary to pass if the condition in the loop is true, then it will break the flow of execution. For more info:

Hope this helps

Hi @Mahmmmoud ,

You could streamline your code by first finding a line that starts with 'From ’ and then splitting and printing words[1].

Hope this helps!

This topic was automatically closed 182 days after the last reply. New replies are no longer allowed.

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• 8.1 Persistence
• 8.2 Opening files
• 8.3 Text files and lines
• 8.4 Reading files
• 8.5 Searching through a file
• 8.6 Letting the user choose the file name
• 8.7 Using try, except, and open
• 8.8 Writing files
• 8.9 Debugging
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• 8.12 Multiple Choice Questions
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• 8.15 Group Work: Reading from Files
• 8.16 Group Work: Reading from CSV Files
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• 8.5. Searching through a file' data-toggle="tooltip" >

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8.4. Reading files ¶

While the file handle object does not contain the actual data in the file, it is quite easy to construct a for loop to read through and count each of the lines in a file:

We can use the file handle object in a for loop. Our for loop simply counts the number of lines in the file and prints them out. The rough translation of the for loop into English is, “for each line in the file represented by the file handle object, add one to the count variable.”

The reason that the open function does not read the entire file is that the file might be quite large with many gigabytes of data. The open statement takes the same amount of time regardless of the size of the file. The for loop actually causes the data to be read from the file.

When the file is read using a for loop in this manner, Python takes care of splitting the data in the file into separate lines using the newline character. Python reads each line through the newline and includes the newline as the last character in the line variable for each iteration of the for loop.

Because the for loop reads the data one line at a time, it can efficiently read and count the lines in very large files without running out of main memory to store the data. The above program can count the lines in any size file using very little memory since each line is read, counted, and then discarded.

Q-2: When using a for loop to read lines, how many lines are read at a time?

If you know the file is relatively small compared to the size of your main memory, you can read the whole file into one string using the read method on the file handle.

In this example, the entire contents (all 94,626 characters) of the file mbox-short.txt are read directly into the variable inp . We use string slicing to print out the first 20 characters of the string data stored in inp .

When the file is read in this manner, all the characters including all of the lines and newline characters are one big string in the variable inp . It is a good idea to store the output of read as a variable because each call to read exhausts the resource:

Remember that this form of the open function should only be used if the file data will fit comfortably in the main memory of your computer. If the file is too large to fit in main memory, you should write your program to read the file in chunks using a for or while loop.

Put the following code in order so that it uses a for each loop to read the file and print out the total number of lines.

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Python data structures: Assignment 8.5

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