1. (more) Python

2. Where we have been

3. Where we have been

4. And where we are going

5. Clojure Python Only values have types Only values have types
Most values are immutable
Some object- orientation, but mostly functional
Mark-and-sweep garbage collection
Only values have types
Some values are mutable
Object-oriented, but with functions as well
Reference-counted garbage collection

6. C++ Python Variables and values have types Identifiers are values
Most values are mutable
Object-oriented, but with functions as well
Scope-based destruction
Only values have types
Identifiers are references
Some values are mutable
Object-oriented, but with functions as well
Reference-counted garbage collection

7. Python Types Integer 42 32-bit (at least) Long integer 42L
Unlimited precision

8. Python Types Real numbers 64-bit double-precision floating point
Generally
you can check with sys.float_info

9. Python Types Complex float values for real and imaginary
1+2j

10. Python Types
String
Either type of quote is usable (as long as you're consistent)
"A string" = 'A string'
'C' is not of type char
Immutable

11. Python Types List Similar to Clojure vector L=[1, 2, 3, 4, 5] Mutable
Slicing
L[0:3] == L[:3] = [1, 2, 3]
L[1:3] == [2, 3]
L[-2:] = [4, 5]
L[-1] == 5

12. Python Types
Tuples
Added to the language to provide an immutable version of the list
T = (1, 2, 3, 4, 5)
Special case for initializing a tuple of length one
T1 = (1,)
Because (1) = 1

13. Python Types Dictionary A hash table
Keys must be hashable and immutable
Mutable
D = {'key1' : 'val1', 2 : [1, 2]}
D['key1'] == 'val1'
D[2] == [1, 2]
Adding elements to the dictionary
D['new-key'] = 'new-val'

14. Significant whitespace
Python (like a few other languages) uses significant whitespace
Bodies of code inside functions, conditional expressions, etc. must have the same indentation
The line before a block ends in a colon

15. Conditionals x = 10 y = 20 if x < y:
print("first condition was true")
else:
print("second condition was true")

16. Functions def function_name(arg1, arg2): print("arg1",arg1)

17. Classes class C: def __init__(self,val): self.val = val
def get_val(self):
return self.val

18. For loops Python doesn't provide a C-style for loop
Instead, it provides something more like the 'range-based' for loop of C++11
for x in ['a', 'b', 'c']:
print(x)
for i in range(10):
for x in {1:'one', 2:'two'}:
print(x)

19. Collection Queries
Collections can be treated as Booleans for the purpose of if and while statements
when doing so, any non-empty collection evaluates to true
L = ['a', 'b', 'c']
while L:
print(L[0])
del L[0]

20. Collection Queries Containment is checked with in L = ['a', 'b', 'c']
if 'z' in L:
print "I found a 'z'!"
D= {1: 'one', 2: 'two'}
if 'two' in D:
print "D had a 'two' in it!"

21. Our old friends: map and filter
Python has a built-in version of the map and filter that you wrote before the midterm

22. Map L = [1, 2, 3, 4, 5] L2 = map(lambda x: x*x, L)
-> [2, 4, 6, 8, 10]

23. Filter L = [1, 2, 3, 4, 5] L2 = filter(lambda x: x%2==0 , L)
-> [2, 4]

24. But don't do that! List comprehensions
The scariest thing about them is the name

25. List Comprehensions
[ <expression> for <var> in <collection>]

26. List Comprehensions: Map
L2 = [x*x for x in L]

27. List Comprehensions: Filter
L2 = [x for x in L if x%2==0]

28. List Comprehensions L = [1, 2, 3, 4, 5]
L2 = [x*x for x in L if x%2==0]

29. List Comprehensions You can even use multiple variables
[(x,y) for x in range(5) for y in range(5) if x<y]