DataCamp中Introduction to Python之Python Basics练习

DataCamp的Introduction to Python之Python Basics是一些比较基础的练习，可以很快掌握。

The Python Interface

In the Python script on the right, you can type Python code to solve the exercises. If you hit Run Code or Submit Answer, your python script (script.py) is executed and the output is shown in the IPython Shell. Submit Answer checks whether your submission is correct and gives you feedback.

You can hit Run Code and Submit Answer as often as you want. If you’re stuck, you can click Get Hint, and ultimately Get Solution.

You can also use the IPython Shell interactively by simply typing commands and hitting Enter. When you work in the shell directly, your code will not be checked for correctness so it is a great way to experiment.

Instructions

Experiment in the IPython Shell; type 5 / 8, for example.
Add another line of code to the Python script on the top-right (not in the Shell): print(7 + 10).
Hit Submit Answer to execute the Python script and receive feedback.

Exercise

# Example, do not modify!
print(5 / 8)# Print the sum of 7 and 10
print(7+10)

Any comments?

Something that Hugo didn’t mention in his videos is that you can add comments to your Python scripts. Comments are important to make sure that you and others can understand what your code is about.

To add comments to your Python script, you can use the # tag. These comments are not run as Python code, so they will not influence your result. As an example, take the comment in the editor, # Division; it is completely ignored during execution.

Instructions

Above the print(7 + 10), add the comment

Exercise

# Division
print(5 / 8)# Addition
print(7 + 10)

Python as a calculator

Python is perfectly suited to do basic calculations. Apart from addition, subtraction, multiplication and division, there is also support for more advanced operations such as:

Exponentiation: . This operator raises the number to its left to the power of the number to its right. For example 42 will give 16.
Modulo: %. This operator returns the remainder of the division of the number to the left by the number on its right. For example 18 % 7 equals 4.
The code in the script gives some examples.

Instructions

Suppose you have $100, which you can invest with a 10% return each year. After one year, it’s dollars, and after two years it’s . Add code to calculate how much money you end up with after 7 years, and print the result.

Exercise

# Addition, subtraction
print(5 + 5)
print(5 - 5)# Multiplication, division, modulo, and exponentiation
print(3 * 5)
print(10 / 2)
print(18 % 7)
print(4 ** 2)# How much is your $100 worth after 7 years?
num =100
for i in range(7):num *= 1.1
print(num)print(100*1.1**7)

Variable Assignment

In Python, a variable allows you to refer to a value with a name. To create a variable use =, like this example:

x = 5
You can now use the name of this variable, x, instead of the actual value, 5.

Remember, = in Python means assignment, it doesn’t test equality!

Instructions

Create a variable savings with the value 100.
Check out this variable by typing print(savings) in the script.

Exercise

# Create a variable savings
savings=100# Print out savings
print(savings)

Calculations with variables

Remember how you calculated the money you ended up with after 7 years of investing $100? You did something like this:

100 * 1.1 ** 7
Instead of calculating with the actual values, you can use variables instead. The savings variable you’ve created in the previous exercise represents the $100 you started with. It’s up to you to create a new variable to represent 1.1 and then redo the calculations!

Instructions

Create a variable growth_multiplier, equal to 1.1.
Create a variable, result, equal to the amount of money you saved after 7 years.
Print out the value of result.

Exercise

# Create a variable savings
savings = 100# Create a variable growth_multiplier
growth_multiplier =1.1# Calculate result
result = savings * growth_multiplier ** 7# Print out result
print(result)

Other variable types

In the previous exercise, you worked with two Python data types:

int, or integer: a number without a fractional part. savings, with the value 100, is an example of an integer.
float, or floating point: a number that has both an integer and fractional part, separated by a point. growth_multiplier, with the value 1.1, is an example of a float.

Next to numerical data types, there are two other very common data types:

str, or string: a type to represent text. You can use single or double quotes to build a string.
bool, or boolean: a type to represent logical values. Can only be True or False (the capitalization is important!).

Instructions

Create a new string, desc, with the value “compound interest”.
Create a new boolean, profitable, with the value True

Exercise

# Create a variable desc
desc = 'compound interest'# Create a variable profitable
profitable =True

Operations with other types

Instructions

Calculate the product of savings and growth_multiplier. Store the result in year1.
What do you think the resulting type will be? Find out by printing out the type of year1.
Calculate the sum of desc and desc and store the result in a new variable doubledesc.
Print out doubledesc. Did you expect this?

Exercise

savings = 100
growth_multiplier = 1.1
desc = "compound interest"# Assign product of growth_multiplier and savings to year1
year1 = savings * growth_multiplier# Print the type of year1
print(type(year1))# Assign sum of desc and desc to doubledesc
doubledesc = desc + desc# Print out doubledesc
print(doubledesc)

Type conversion

Hugo mentioned that different types behave differently in Python.

When you sum two strings, for example, you’ll get different behavior than when you sum two integers or two booleans.

In the script some variables with different types have already been created. It’s up to you to use them.

Instructions

Hit Run Code to run the code. Try to understand the error message.
Fix the code such that the printout runs without errors; use the function str() to convert the variables to strings.
Convert the variable pi_string to a float and store this float as a new variable, pi_float.

Exercise

# Definition of savings and result
savings = 100
result = 100 * 1.10 ** 7# Fix the printout
print("I started with $" + str(savings) + " and now have $" + str(result) + ". Awesome!")# Definition of pi_string
pi_string = "3.1415926"# Convert pi_string into float: pi_float
pi_float=float(pi_string)