Use Python 2.7 from
.py(this will enable syntax coloring).
Try it with this first program:
print "Hello world." # Lines that start with a "#" are called comments. # You can type whatever you want there, python ignores them.
Named location to store data. Names cannot have spaces in them. They are case-sensitive (upper/lower). Names can have numbers, but cannot start with numbers —
quiz 3(due to space)
3rdquiz(can’t start with number)
It’s okay to have underscore character instead of a space:
x = 14 # evaluate right side of equal sign, y = x * 2 # put that value in the variable on the left. x = x - 4 # At this point, x holds 10 and y holds 28.
print "Testing!" # Quotes indicate a string of characters (text) print "x+1" # Variables, arithmetic not evaluated inside quotes print x+1 # Performs variable lookup and addition. print "The answer is", y # Combine multiple parts on one line.
name = raw_input("Your name:") # Prompt in quotes and parentheses. # Result of what user typed assigned to variable on the left. print "Your name is", name # raw_input returns a string of characters (text). # If you want a number, convert it using int() or float(). # int for integer (whole numbers) # float for floating-point (decimal numbers) score = int(raw_input("Enter score:")) print "Twice that score is", score*2
If shell window appears messed up, not responding, try control-C a few times.
Try to write a program that will behave something like the following. (The user types in the text after the colon on the first two lines.)
Enter your name: Alice Enter the year you were born: 1984 Alice, you are about 28 years old.
# Python has True and False (Boolean values). # 3 < 4 produces True # 3 == 4 produces False (are these equal?) # Note the use of '==' for equality, not '=' which is assignment if y < 30: # colon required print "That's small." # only happens if y < 30. y = y + 10 if y < 30: print "This does not happen." else: print "This does happen, because y is now big."
In addition to less than (
<), greater than (
>), and equal to (
==), you can use less-than-or-equal-to (written in mathematics as ≤ but in Python as
<=) or greater-than-or-equal-to (
temp = float(raw_input("Enter temperature:")) if temp < 40: print "That's cold!" else: if temp > 90: print "That's hot." else: print "That's comfortable."
We previously learned the Boolean operators and, or, not. You can directly apply these in your Python programs. For example, to check whether a temperature is between 60 and 80:
if temp >= 60 and temp <= 80: print "What a mild day!"
This is an extension of the previous exercise, that computed a person’s age based on the birth year (by subtracting from the current year, 2012).
In this one, you should print a message at the end that depends on the decade of the user’s birth. So, that’s done with a condition, or a series of conditions.
Here is one example:
Enter your name: Chris Enter the year you were born: 1973 Chris, you are about 39 years old. Dig it, man.
You can come up with your own messages that characterize each decade, but here are some suggestions: