Links: PYTHON - PROGRAMMING
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contents:
- > statements
- > conditions and control flow
- > more operators
- > more looping
any individual line of code itself is commonly called a statement, such as each time we're setting a variable here:
>>> x = 'some text'
>>> y = 12
>>> z = 3.4
a conditional statement can be created by using the keywords if or while, and extended by and and/or or. A bool True value to the overall statement allows the following indented code statement(s) to run.
if
>>> x = 'some text'
>>> if type(x) == str:
... print('this will print.')
...
this will print.
if False:
break
while
>>> l = [1,2,3,4,5,6,7,8,9,10]
>>> while l:
... print("curr list status: ", l)
... l.pop()
...
curr list status: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
10
curr list status: [1, 2, 3, 4, 5, 6, 7, 8, 9]
9
curr list status: [1, 2, 3, 4, 5, 6, 7, 8]
8
curr list status: [1, 2, 3, 4, 5, 6, 7]
7
curr list status: [1, 2, 3, 4, 5, 6]
6
curr list status: [1, 2, 3, 4, 5]
5
curr list status: [1, 2, 3, 4]
4
curr list status: [1, 2, 3]
3
curr list status: [1, 2]
2
curr list status: [1]
1
>>> print(l)
[]
and and or
>>> x = 'some text'
>>> y = 2
>>> if isinstance(x, str) and y == 2:
... print('this will print.')
...
this will print.
>>> if isinstance(x, str) or y == 9000:
... print('this will print.')
...
this will print.
pass
allows for a conditional statement to do nothing without breaking.
>>> x = 'some text'
>>> if x:
... pass
...
>>> # nothing happened {: id="nothing-happened" }
>>> # but, we didn't get an {: id="but,-we-didn't-get-an" }
>>> # IndentationError {: id="indentationerror" }
>>> if x:
...
File "<stdin>", line 2
^
IndentationError: expected an indented block
is
Where the == operator returns True for an equivalent object, the keyword is (by itself) only returns True for the same object.
>>> x = 'some text'
>>> y = 'some text'
>>> z = x
>>> x == y
True
>>> x is y
False
>>> x is z
True
>>> z is x
True
>>> id(x)
140537665644592
>>> id(z)
140537665644592
>>> x = 'some NEW text'
>>> z
'some text'
>>> x is z
False
>>> z = 'some NEW text'
>>> x is z
False
elif
a conditional statement can be extended to handle for additional potential (specific) conditions via elif,
>>> x = 'some text'
>>> if isinstance(x, int):
... print('x is an integer.')
... elif isinstance(x, float):
... print('x is an float.')
... elif isinstance(x, str):
... print('x is a string.')
...
x is a string.
else
a conditional statement can be extended to handle for anything else not specified via it's initial if or any of it's child elif:
>>> class MyThing:
... pass
>>>
>>> x = MyThing()
>>> if isinstance(x, int):
... print('x is an integer.')
... elif isinstance(x, float):
... print('x is a float.')
... elif isinstance(x, str):
... print('x is a string.')
... else:
print('x is something other than int, float, or string...')
x is something other than int, float, or string...
=, ==, ...
+ addition
- subtraction
*multiplication
**exponentiation
/ division
% modulus (remainder division)
>>> 2 + 2
4
>>> 4 - 2
2
>>> 2 * 4
8
>>> 4 ** 2
16
>>> 4 / 2
2.0
>>> # ^^ int division {: id="^^-int-division" }
>>> # results in float {: id="results-in-float" }
>>> 4 % 2
0
>>> 4 % 3
1
>>> # ... {: id="..." }
>>> # order of operations: {: id="order-of-operations:" }
>>> ((2 - 2) * 4) - 2
-2
>>> ((2 - 2) / 4) - 2
-2.0
>>> 4 * ((2 + 2) + (4 / 2))
24.0
>>> 4 * ((2 + 2) + 4 / 2)
24.0
>>> 4 * (2 + 2) + 4 / 2
18.0
>>> 4 * (2 + 2 + 4 / 2)
24.0
Looping is walking through an iterable. We did this above with l = [1,2,3,4,5,6,7,8,9,10] and our conditional statement while l: (so called, a "while loop").
for and in are keywords that can be used together to loop through iterables (such as the builtin containers list and dict):
>>> l = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> for x in l:
... print(x)
...
1
2
3
4
5
6
7
8
9
10
>>> d = {'a':1, 'b':2, 'c':3, 'd':4}
>>> for k,v in d.items():
... print('the key:', k, 'the val:', v)
...
the key: a the val: 1
the key: b the val: 2
the key: c the val: 3
the key: d the val: 4
>>> # ... {: id="..." }
>>> for k in d.keys():
... print('the key only:', k)
...
the key only: a
the key only: b
the key only: c
the key only: d
>>> # ... {: id="..." }
>>> for v in d.values():
... print('the val only:', v)
...
the val only: 1
the val only: 2
the val only: 3
the val only: 4
str, int, float,
list, dict,
...
set
>>> l = [1,2,2,2,2,3,2]
>>> set(l)
{1, 2, 3}
tuple
>>> l = [1,2,2,2,2,3,2]
>>> tuple(l)
(1, 2, 2, 2, 2, 3, 2)
>>> l = tuple(l)
>>> l.pop()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'tuple' object has no attribute 'pop'
>>> # one does not simply {: id="one-does-not-simply" }
>>> # change an immutable data type {: id="change-an-immutable-data-type" }
a function is a collection of statements, initialized by the keyword def, commonly serving a specific (single) purpose, defined as such for re-usability and generalization.