Practice Python

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Beginner Python exercises

06 December 2014

Read From File

Exercise 22 (and Solution)

Given a .txt file that has a list of a bunch of names, count how many of each name there are in the file, and print out the results to the screen. I have a .txt file for you, if you want to use it!




  1. Reading a file
  2. Dictionaries

Reading a File

Reading a file is very analogous to writing a file, as I discussed before in Exercise 21. But, the best source is always the official Python 3.3 documentation.

Simply, reading to a file takes two steps:

  1. Opening the file for reading
  2. Read!

Opening a file for reading is the same as opening for writing, just using a different flag:

  with open('file_to_read.txt', 'r') as open_file:
    all_text =

Note how the 'r' flag stands for “read”. The code sample from above reads the entire open_file all at once into the all_text variable. But, this means that we now have a long string in all_text that can then be manipulated in Python using any string methods you want.

Another way of reading data from the file is line by line:

  with open('file_to_read.txt', 'r') as open_file:
  	line = open_file.readline()
  	while line:
    	line = open_file.readline()

Instead of print(line), you can imagine doing anything you want to the line of text… If you save it to a variable, you have a string that you can then use something like .strip() or .split() with.


Dictionaries are Python’s way of associating two pieces of data together. The official documentation says it all.

  student_scores = {'Adama': 100, 'Starbuck': 75, 'Apollo': 80, 'Athena': 85, 'Agathon': 90}

The strings (or whatever happens to the left of the : sign), are called keys. When I want to access the values (the things to the right of the : sign), I need to ask the dictionary for the value associated with the key:

  adama_score = student_scores['Adama']

You can then modify the score and save it back to the dictionary:

  adama_score = student_scores['Adama']
  adama_score += 100	% adama_score is now 200. This doesn't change the dictionary value
  student_scores['Adama'] = adama_score		% the score in the dictionary is now updated

I can’t ask the dictionary for the key associated with a value, but I can get a list of all the keys, and the same for all the values:

  all_scores = student_scores.keys()
  all_names = student_scores.values()

I can use the in keyword (just like in lists), do dictionary comprehensions like list comprehensions (these are cool, take a look at the official bit about these), and iterate over the elements in the dictionary (the syntax is just a little bit different).

  for pair in student_scores.items():

And this prints out pairs of keys and values that look like: (Adama, 100), etc.

Because dictionaries are not ordered, looping through them does not guarantee the key / value pairs coming out in a particular order. So be careful.


Happy coding!

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