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Scripting Languages
Python basics
Interpreter
●
direct conversation (terminal command: python)
●
version, help, modules
●
experiments with numbers and variables
Python
Python 2.7.12
2.7.12 (default,
(default, Jul
Jul 11 2016,
2016, 15:12:24)
15:12:24)
[GCC
[GCC 5.4.0
5.4.0 20160609]
20160609] on
on linux2
linux2
Type
Type "help",
"help", "copyright",
"copyright", "credits"
"credits" or
or "license"
"license"
for
more
information.
for more information.
>>>
>>> 2+2
2+2
44
>>>
>>> 2.0+2.0
2.0+2.0
4.0
4.0
>>>
>>> 2**32
2**32
4294967296
4294967296
>>>
>>> aa == 10
10
>>>
>>> a**2
a**2
100
100
Numbers
●
No declaration needed
●
Numerical data types:
–
integer “int”
●
●
●
–
float
●
–
●
64bit → ±9,223372,036854,775807
or “long” for very big ones
for integer division always use //
use dot: 1.0, 2.0, 0.1, etc.
complex (you will not need this now)
Type check:
–
type()
●
Mixing types in calculation
●
Automatic type conversion
>>>
>>> 1024*1024
1024*1024
1048576
1048576
>>>
>>> 2**64
2**64
18446744073709551616L
18446744073709551616L
>>>
>>> 3/2
3/2
11
>>>
>>> 3//2
3//2
11
>>>
>>> 3.0/2.0
3.0/2.0
1.5
1.5
>>>
>>> (1+1j)*(1-1j)
(1+1j)*(1-1j)
(2+0j)
(2+0j)
>>>
>>> xx == 17
17 -- 2.0
2.0
>>>
>>> type(x)
type(x)
<type
<type 'float'>
'float'>
Numerical type conversion
●
Use int(), float() for changing the type
–
int()
→ float()
–
float() → int()
fraction will be lost !
>>>
>>> aa == 33
>>>
>>> 11 ++ float(a)
float(a)
4.0
4.0
>>>
>>> bb == 1.5
1.5
>>>
>>> 11 ++ int(b)
int(b)
22
>>>float(int(3.3))
>>>float(int(3.3))
3.0
3.0
Names, Assignment, Expression
x_1=(10 + y)*3.0
name assignment expression
●
●
Name( Variable )
case-sensitive
–
must start with a letter
–
space and ()[]{}+-/*” are not allowed
Assignment operator: single “=”
–
●
aa == 22
–
multiple assignments allowed
Expression
–
values, variables, operators
–
operators priority: **, -, */,+-
–
brackets
ii == jj == kk == 0.0
0.0
x,
x, y,
y, zz == 1,
1, 2,
2, 33
X,
X, yy == y,
y, xx
-2**2 ≠ (-2)**2
Exercise
●
Temperature conversion:
–
variables: c, k, f (Celsius, Kelvin, Fahrenheit)
cc == 77
kk == ...
...
ff == ...
...
print
print c,
c, k,
k, ff
Strings
●
Data type: a sequence of characters
–
Single quotes: 'string', 'may contain double" '
–
Double quotes: "string", "may contain single' "
●
Escape: '\'', "\"",
–
triple quotes '''…''' or """…""", may include
single&double quotes and newlines (\n)
aa
bb
cc
dd
ee
==
==
==
==
==
"123"
"123"
'1+2+3'
'1+2+3'
"12\"35'"
"12\"35'"
'12"35\''
'12"35\''
"""12"35"""
"""12"35"""
aa == '''
'''
this
this can
can be
be
any
any long
long text
text
in
in many
many lines
lines
'''
'''
String properties
●
Operations on strings: help(str)
–
len(s)
–
s1 + s2
–
s.isdigit()
–
s.isalpha()
–
s.upper()
–
s.lower()
–
and others
>>>
>>> aa == "Hello"
"Hello"
>>>
>>> len(a)
len(a)
55
>>>
>>> a.isdigit()
a.isdigit()
False
False
>>>
>>> a.upper()+a.lower()
a.upper()+a.lower()
'HELLOhello'
'HELLOhello'
>>>
>>> type(a)
type(a)
<type
<type 'str'>
'str'>
String slicing
●
●
Numbered sequence
–
string
–
position
s="Hello"
01234
Substrings: [ ]
–
first char at position 0
–
last char at position -1
–
access range with ":"
●
0:n means n chars,
–
from 0 to n-1 position
>>>
>>> xx == "Hello
"Hello world"
world"
>>>
>>> x[0]
x[0]
'H'
'H'
>>>
>>> x[0:4]
x[0:4]
'Hell'
'Hell'
>>>
>>> x[:4]
x[:4]
'Hell'
'Hell'
>>>
>>> x[:]
x[:]
'Hello
'Hello world'
world'
>>>
>>> x[-1]
x[-1]
'd'
'd'
>>>
>>> x[3:-1]
x[3:-1]
'lo
'lo worl'
worl'
>>>
>>> x[-4:-1]
x[-4:-1]
'orl'
'orl'
>>>
>>> x[-4:]
x[-4:]
'orld'
'orld'
String formatting
●
Gluing together strings and numbers
–
string.format("pattern",args)
–
{n} for argument placement and position
–
d,f,s for int, float and string types
>>>
>>> aa == "I'm
"I'm {0}
{0} and
and
>>>
>>> print
print aa
I'm
I'm John
John and
and I'm
I'm 20
20
>>>
>>> print
print "T={0:2d}C
"T={0:2d}C
T=
T= 1C
1C is
is +274.1500K
+274.1500K
I'm
I'm {1}".format('John',20)
{1}".format('John',20)
is
is {1:+.4f}K".format(1,274.15)
{1:+.4f}K".format(1,274.15)
https://docs.python.org/2/library/string.html#format-specification-mini-language
Logic data type: bool
●
Only two values:
–
●
True or False
Operators:
–
comparisons:
●
–
==, !=, <, <=, >, >=
logic operators:
●
not, and, or
>>>
>>> 1==2
1==2
False
False
>>>
>>> True==1
True==1
True
True
>>>
>>> a,b,c
a,b,c == 1,2,3
1,2,3
>>>
>>> a<0
a<0 or
or b>c
b>c and
and
False
False
>>>
>>> a<0
a<0 or
or b<c
b<c and
and
True
True
>>>
>>> dd == a<0
a<0 or
or b<c
b<c
>>>
>>> dd
True
True
>>>
>>> type(d)
type(d)
<type
<type 'bool'>
'bool'>
c>2
c>2
c>2
c>2
and
and c>2
c>2
Comments
●
Comments start with hash ‘#’ character
●
‘#’ must be the first (non-white) character
●
Everything after ‘#’ is ignored till the end of line
●
Use comments in your code !
##
ww
ww
==
–– width
width
10
10
##
ll
ll
==
–– length
length
20
20
##
aa
aa
==
––
ww
area
area
** ll
Taking decisions → if-elif-else
–
conditions are bool-type followed by ‘:’
–
body instructions are indented (use 4-spaces)
if cond :
instr
if
if a>0:
a>0:
print
print
else:
else:
print
print
if cond :
instr1
else:
instr2
"positive"
"positive"
"not
"not positive"
positive"
if cond1 :
instr1
elif cond2 :
instr3
else:
instr3
if
if a>0:
a>0:
print
print
elif
elif a<0:
a<0:
print
print
else:
else:
print
print
"positive"
"positive"
"negative"
"negative"
"zero"
"zero"
Conditional loop → while
–
condition bool-type in the first line
●
–
in Python there is no loop with condition at the end
(nothing like do-while exists)
body indented
while cond :
instr
while
while
ii
jj
ii
==
==
<< j:
j:
i+1
i+1
j-1
j-1
Exercise - factorial
–
Factorial n! = n∙(n-1)∙...2∙1
●
●
●
how far you can go with value of n?
what is the data type of result ‘s’?
how many digits has 100!
start
n = …
s = n
False
print s
stop
n>1
True
n = n-1
s = s*n
Loop control →break, continue
●
break →immediate escape from the loop
●
continue →immediate start of the next cycle
while cond1 :
if cond2:
break
instr
aa == 00
while
while aa << 10:
10:
aa == a+1
a+1
if
if a**4
a**4 >> 1000:
1000:
break
break
print
print a,
a, a**4
a**4
while cond1 :
if cond2:
break
instr
aa == 11
11
while
while aa >> -10:
-10:
aa == a-1
a-1
if
if a==0:
a==0:
continue
continue
print
print a,
a, 1.0/a
1.0/a
Exercise – guest-it game
start
goal=…
goal
goal == ……
while
while True:
True:
read
readguess
guess
if
if ……
print
print
elif
elif ……
print
print
else
else
print
print
break
break
True
True
guess
……
False
……
guess>goal
True
"too big"
……
guess<goal
"got it"
stop
True
"too big"
Getting input
●
s = raw_input("prompt")
–
print a "prompt" message and return input
–
always the string-type is returned
–
s.isdigit() → make sure there are digits only
–
n = int(s) → convert to integer
while
while True
True
ss == raw_input("Number
raw_input("Number ->
-> ")
")
if
if not
not s.isdigit():
s.isdigit():
continue
continue
nn == int(s)
int(s)
……
Random values
●
Add a library (module) to your program
–
●
Use function from the module
–
●
import random
random.function()
Read documentation
–
Python 2 Standard Library
●
9. Numeric and Mathematical Modules
–
9.6. random — Generate pseudo-random numbers
● random.randint(a, b)
Return a random integer N such that a <= N <= b
import
import random
random
……
guess
guess == random.randint(1,100)
random.randint(1,100)
Math functions
●
Add a library (module) to your program
–
●
import math
Read documentation
–
Python 2 Standard Library
●
9. Numeric and Mathematical Modules
–
9.2. math — Mathematical functions
import
import math
math
……
xx == math.sqrt(math.cos(2*math.pi/T)**2
math.sqrt(math.cos(2*math.pi/T)**2 -1)
-1)