Exercise 0 LSE Home

In this exercise, you are asked to write a simple Python function to count the number of words in a text. To complete this task, it would be useful to identify which characters in a string are whitescape that separates words (that is, consecutive non-whitespace characters).

You can use the following function, which helps you detecting whitespace, that is a space or tab or similar character in a string. For a String or a character variable text, you can find out whether the String or the character is a whitespace by using

text.isspace()

This expression returns true or false.

Exercise 0.1. Write a Python function wordCount(text) in a file named Wordcount.py that counts the words of a text given as an argument to the function. For simplicity, we count everything as a word which does not contain whitespaces but is preceded and followed by one or several whitespaces (exceptions are the first and the last word of the text, which may only have one surrounding whitespace). For example,

wordcount(" How many words\ \ \ \ does this text have? ")

should output 7, but

wordcount("How many words does this text have ?")

should output 8.

(Do not use any Python library function other than isspace(), but rather find an algo- rithm yourself.)

Hint: This task may come challenging (if you are new to Python). So, first, ignore the possibility that several whitespaces can occur consecutively in the text, and assume that two words are always separated by only one whitespace. If this works correctly, then change your program so that it can also deal with consecutive whitespaces.

Do not forget to test your program with some small and some large examples of strings to cover different cases that need to handled, to see whether it works correctly.

You may find that using while loops instead of for loops is more intuitive. If you have not come accross while loops before, you can read about them here:

• https://docs.python.org/3/tutorial/introduction.html#first-steps-towards-programming
• https://docs.python.org/3/reference/compound_stmts.html#while

This homework also gives you a chance to practise writing your code and running it in an environment other than the online tutorial environment at Dataquest. The first (of four) tutorial documents and the section “Python Resources” on MA407 Moodle site give some instructions on to set up and use Python on your and LSE computers.

Solving Task 0.1 is, in fact, also your first piece of formative assessment for MA407. In MA407, you are required to submit solutions to problem sets on a platform called Gradescope. Further instructions on how to submit your program will be provided during the first week of the term. For now, you can concentrate on completing the task.

You should be submitting a single file called Wordcount.py that should include the definition of the function wordcount(text). The accurate naming of the Python functions and files are crucial for the automatic submission and marking processes on Gradescope.

Submit your solutions before 2pm (London time) on 29 September 2023.

Include your name, student number in each file. Good luck!

1. 修改列表但不返回

当你在函数内部直接修改传入的列表，并且没有返回任何东西时，由于列表是可变对象，所做的修改将影响原始列表。

def append_value(lst, value):
    lst.append(value)

my_list = [1, 2, 3]
append_value(my_list, 4)
print(my_list)  # 输出 [1, 2, 3, 4]

即使 append_value 函数没有 return 语句，它仍然修改了 my_list 的内容。

2. 修改列表并返回

在某些情况下，你可能希望在函数内部创建一个新的列表，进行修改，并返回这个新列表，而不影响原始列表。

def add_lists(lst1, lst2):
    return lst1 + lst2

list1 = [1, 2, 3]
list2 = [4, 5, 6]
new_list = add_lists(list1, list2)
print(list1)     # 输出 [1, 2, 3]
print(new_list)  # 输出 [1, 2, 3, 4, 5, 6]

在这个例子中，add_lists 函数返回了一个新的列表，原始的 list1 并没有被修改。

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