# Convert from Fahrenheit to Celsius
degreesF, degreesC = 0, 0
degreesF = float(input('Enter the temperature in degrees F: '))
degreesC = 5/9*(degreesF - 32)
print(degreesF, 'degrees F =', degreesC, 'degrees C')
print(degreesF, 'degrees F = {:10.3f}'.format (degreesC), 'degrees C')
print('Please enter some text:')
x = input()
print('Text entered:', x)
print('Type:', type(x))
print('Please enter a number:', end='\n')
s1 = input()
print('Please enter another number:', end='\n')
s2 = input()
n1 = int(s1)
n2 = int(s2)
print(n1, '+', n2, '=', n1 + n2)
n1 = int( input( 'Enter number one:' ))
n2 = int( input( 'Enter number two:' ))
print(n1, '+', n2, '=', n1 + n2)
n1 = int(float( input( 'Enter number one:' )))
n2 = int(float( input( 'Enter number two:' )))
print(n1, '+', n2, '=', n1 + n2)
a,b,c,d,e = 2,4,7,9,31
print (a,b,c,d,e)
print (a,b,c, end=' / ')
print (d,e, sep=':::')
print ('s'*20)
print('{0} {1}'.format(0, 10**0))
print('{0} {1}'.format(1, 10**1))
for i in range(10):
print ('{0:>3} {1:>16}'.format(i, 10**i))
str = '''
This is a multiple lines
comments
# ! {} @
'''.format( "what have you" )
print ( str )
cubes = [] for i in range(5): cubes.append(i**3) cubes = [i**3 for i in range(5)] print (cubes) cubes = [i**3 for i in range(30) if i % 3 == 0] print (cubes)
cities = { 'United States': 'San Jose', 'France': 'Paris', 'Italy': 'Rome' }
cities_transposed = { cities[key]: key for key in cities }
print (cities_transposed)
[ i**2 for i in range(8) ] sum( i**2 for i in range(8) ) sum([ i**3 for i in range(8) ]) min([ i**3 for i in range(8) ]) max([ i**3 for i in range(8) ]) print ( sum( i**3 for i in range(8) ))
cities = { 'United States': 'San Jose', 'France': 'Paris', 'Italy': 'Rome' }
cities['Italy']
# merge two dictionaries
more = {'Germany': 'Berlin', 'United Kingdom': 'London'}
cities.update( more )
# adding
cities['Spain'] = 'Madrid'
try:
cities['Germany']
except:
print ('No Germinay city specified')
'Germany' in cities
# False
'Italy' in cities
# True
# delete items
del cities['United States']
# loop over dict for key in cities: print (key, cities[key]) for key in cities.keys(): print (key, cities[key]) for value in cities.values(): print (value) for key,value in cities.items(): print (key, value)
import os
import shutil
from os import path
from shutil import make_archive
from zipfile import ZipFile
# make a duplicate of an existing file
if path.exists ("w1.txt"):
# get the path to the file in the current directory
src = path.realpath ("w1.txt")
# separate the path part from the filename
fpath, fname = path.split (src) ## :h :t
print ( "path:", fpath )
print ( "file:", fname )
# let's make a backup copy by appending "bak" to the name
dst = src + '.bak'
# now use th eshell to make a copy of the file
shutil.copy (src,dst)
# copy over the permissions, modification times, and other info
shutil.copystat (src,dst)
# rename the original file
os.rename ("w1.txt", "new.txt")
# common use
os.getcwd()
os.chdir()
os.remove('file_to_remove.txt')
# now put things into a ZIP archive
fpath, fname = path.split (src) ## :h :t
shutil.make_archive ("archive", "zip", fpath)
# more fine_grained constrol over ZIP files
with ZipFile ("w1.zip", "w") as newzip:
newzip.write ("new.txt")
newzip.write ("w1.txt.bak")
os.system( "/bin/cp w1.txt.bak w1.txt" )
import os print (os.name) ## always posix for linux, windows or OS X import platform platform.platform()
import os.path
os.path.join ('path_name', 'sub_path', 'file_name')
>>> 'path_name/sub_path/file_name'
## on window system
os.path.join ('c:','path_name', 'sub_path', 'file_name')
>>> 'path_name\sub_path\file_name'
os.path.exists ('path_or_file_name')
os.path.isfile ('path_or_file_name')
os.path.isdir ('path_or_file_name')
os.path.islink ('path_or_file_name')
import os filename = 'book.txt' cmd = 'ls '+ filename fp = os.popen( cmd ) res = fp.read() stat = fp.close()
friends = ["amy", "david", "stella", "niyu", "vivek", "michael"]
print (friends)
print (friends[0])
print (len(friends) )
for i in range(len(friends)):
friends[i] += " smith"
print ( friends )
for i in range(len(friends)):
friends[i] = "none"
print ( friends )
mixarray = [ 1, [9,8], (3,4), 'letter', {0:'first'}, 2, 5, 25 ]
mixarray[3]
mixarray[:3]
mixarray[-3:] # last three elements
mixarray[8:8] = [88,99] # insert after the last,
# notice mixarray[8] would error out
mixarray[2:5] = [22,55] # replace the elements,
# notice the length does not have to match
# array method: append, remove, extend, pop, sort, index, reversed
a = [2,3,4]
b = ['two','three','four']
h = zip(a, b)
mixarray.append( 'dog' ) print (mixarray) mixarray.extend( 'cat' ) print (mixarray) mixarray.extend( [ 'cat' ] ) print (mixarray) mixarray += 'pig' print (mixarray) mixarray += [ 'pig', 'donald duck' ] print (mixarray)
filename = r"C:\dir\new"
filename = 'C:\\dir\\new'
filename = 'C:/User/myname/dirname'
a = ['amy','smith']
s = ' '.join(a)
s.join(" baz")
n = len(s)
mixarray[2:3] print (mixarray[5:]) mixarray[:8] print (mixarray[4:-1]) print (mixarray[-1]) print (mixarray[:]) ## the while array mixarray[2:4] = ['new1', 'new2'] ## this replace [2] [3] print (mixarray) mixarray[2:3] = ['new3', 'new4'] ## this replace mixarray[2] with two elements 'new3', 'new4' print (mixarray) newary = mixarray[:] ## copy the whole array newbry = mixarray[-2:] ## last 2 elements newcry = mixarray[::-1] ## reverse the whole array s = 'xxyyzzppqqmm' t = s[slice(None,None,-1)] ## same as s[::-1]
del mixarray[-2:] ## this delete the last 2 elements
print (mixarray)
mixarray.insert( 2, 'monkey' )
print (mixarray)
del mixarray[2]
mixarray.remove ('donald duck')
print (mixarray)
import
for i in mixarray:
print ( i, end=' ' )
print()
for k,v in enumerate (mixarray):
print ( k, ':', v, end=' / ' )
print()
from collections import Counter
Counter(mixarray)
# Counter(mixarray) # this will error out
s = "this is a string, a very long string"
Counter(s)
Counter(s[0])
f = open ("myfile.txt", "r")
if f.mode == "r":
data = f.read() ## read the whole file
line = f.readline() ## read a line
f = open ("myfile.txt", "w")
for i in range (10):
f.write ( i, "line" )
# append more lines
f = open ("myfile.txt", "a")
f.write ("That's all")
f.close()
data = open ("myfile.txt").read() ## return whole file as one single string
data = open ("myfile.txt").readline() ## return one line as a string
data = open ("myfile.txt").readlines() ## return whole file as list of strings, with '\n'
f = "myfile.txt"
with open( f ) as fh:
lines = list( map( str.rstrip, fh.readlines() ))
from datetime import date
from datetime import time
from datetime import datetime
## Using objects of class type date, time, datetime
today = date.today()
print ( "Today's date is", today )
print ( "Today :", today.month, today.day, today.year )
weekday = "Sunday" if today.weekday() == 6 else ""
weekday = "Monday" if today.weekday() == 0 else weekday
weekday = "Tuesday" if today.weekday() == 1 else weekday
weekday = "Wednesday" if today.weekday() == 2 else weekday
weekday = "Thursday" if today.weekday() == 3 else weekday
weekday = "Friday" if today.weekday() == 4 else weekday
weekday = "Saturday" if today.weekday() == 5 else weekday
print ( "Today : {} / {}-{}-{}".format ( weekday, today.month, today.day, today.year ))
today = datetime.now()
print ( "Now is", today )
days = [ "Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun" ]
wkday = date.weekday (today) ## returns the same as today.weekday()
print ( "Today : {} / {}-{}-{}".format ( days[wkday], today.month, today.day, today.year ))
print ( today.strftime ("%Y") ) ## full year, ex. 2019
print ( today.strftime ("%a") ) ## abbreviated day, ex. Tue
print ( today.strftime ("%d") ) ## day number, ex. 18
print ( today.strftime ("%B") ) ## full month, ex. December
print ( today.strftime ("%y") ) ## abbreviated year, ex. 19 for year 2019
print ( today.strftime ("%c") ) ## locale's date and time, ex. Tue Dec 18 21:36:09 2019
print ( today.strftime ("%x") ) ## locale's date, ex. 12/18/19
print ( today.strftime ("%X") ) ## locale's time, ex. 21:36:09
print ( today.strftime ("%A, %d %b, %Y") ) ## prints "Tuesday, 18 Dec, 2018"
# for time formatting #
# %I/%H - 12/24 hour system, %M - minute, %S - second, %p - locale's AM/PM
print ( today.strftime ("%H:%M:%S %p") ) ## 24-Hour:Minute:Second:AM/PM
print ( today.strftime ("%I:%M") ) ## 12-Hour:Minute
# timedeltas #
from datetime import timedelta
print ( "One year from today :", datetime.now() + timedelta (days=365) )
print ( timedelta (days=222, hours=3, minutes=4) )
print ( "Today:", datetime.now() )
print ( "3 weeks and 3 days from now :", datetime.now() + timedelta(weeks = 3, days=3) )
print ( "3 weeks and 3 days from now :" + str(datetime.now() + timedelta(weeks = 3, days=3)) )
# how many days till Halloween
t1 = datetime.now() - timedelta(weeks=2)
t1str = t1.strftime ("%A %B %d, %Y")
print ( t1str + " is two weeks old." )
# how many days till Halloween
today = date.today()
halloween = date(today.year, 10,30)
if halloween < today:
print ( "Halloween has passed by {} days".format( (today - halloween).days ))
halloween = halloween.replace (year=today.year + 1)
time_to_halloween = abs(halloween - today)
print ( "There are", time_to_halloween.days, "more days to Halloween." )
import calendar
# To start the calendar on Sunday as first column
c = calendar.TextCalendar (calendar.SUNDAY)
cstr = c.formatmonth (2019, 1, 0, 0)
print (cstr)
# returns multiple '0', say two '0' if 2019/1/1 starts on Tuesday
for i in c.itermonthdays (2019, 1):
print (i)
for name in calendar.month_name:
print (name)
for name in calendar.day_name:
print (name)
ta = datetime.datetime (year=2018, month=1, day=1)
tb = datetime.datetime (year=2018, month=2, day=1)
tb-ta
ta-tb
print (tb-ta)
You learn the syntax and write some code. You learn the fundamentals and then you hit a wall.
Before you take off, just bear with me a few more lines and see if you are still interested.
Just type any code, any code and you feel like progress and it's an easy emotional hit, but it's an illusion. You think you can suss out everything along the way and just go by the seat of the pants. Sometimes that works, right?
How many of those code written this way are you still using?
It is about creating better and more complex applications, writing code faster with less pain, less bugs. It's about "future proof" and future proof means to be flexible, maintainable and extensible for new changes to come.
Maybe the first thing that comes to your mind is, "now what do I do?", when the blinking cursor in the IDE editor is daring you. Maybe you are seasoned programmer and you jump right to coding. Good software starts with good designs. It's time to grab some paper and pencil.
You need something you can write on the back of a napkin and understand how to break it into right pieces. Then you know exactly what code to write.
Terminology is not a formalized fixed way of thinking. It is necessary for communication in any professions. Think of chefs using cooking terms, musicians using chord, scales and symbols, we need a system to speak to our fellow programmers too. Knowing the right vocabulary saves us time from making silly mistakes, and from explaining the same ideas over and over again.
Okay then, what is Object-oriented? What is Class, Object, Instance? What is Polymorphism, Abstraction, Encapsulation, and blah? I think we need a good night sleep before we open the can of worms. Time for a break.
# Example class
class Animal():
def whoami (self):
print ("I am an animal.")
def sound_like (self, string):
print ("Animal sounds like: " + string)
def get_limps (self, i):
print ("Animal has " + i + " limps.")
a = Animal()
a.whoami()
# Example class inheritance
class Dog (Animal):
def whoami (self):
Animal.whoami (self)
super().whoami()
print ("I am a Dog!")
b = Dog()
b.whoami()
# Example Loops
# this loop from 0 to 99
for i in range (100):
print ( i )
# range (a,b) will loop from a to b
# and a must be less than b
for i in range (3,5):
print ( i )
# What is 3 doing here? Three is a crowd, or not?
for i in range (10,20,3):
print ( i )
# Break or continue? That is the question.
for i in range ( 0, 9 ):
if ( i == 7 ): break
if ( i % 2 == 0 ): continue
# Lazy Ann's version
for i in range(10):
if i == 7: break
if i%2: continue
# Look! I can do days too!
days = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" ]
for d in days:
print ( d )
# Python has while loop too.
i = 0
while i < 3:
print ( i )
i += 1
## Remember, python does not do "i++"
while True:
print ( "I am in loop!" )
if True:
break
## See? You have to break it otherwise it goes on and on and on...
# No, python does not have do while loop
# But it has something cool called 'enumerator'
for i, d in enumerate (days):
print (i, d)
# descinding
for i in range (9,1,-1):
print (i)
x = range(10)
z = list(range(10))
y = list( 10-i for i in x )
print (x)
print (z)
print (y)
# Example conditionals
## Some new tricks, one line
print ("foo" if True else "bar")
a = 3 if i == 4 else 99
i = 3
if i in [ 1,2,3 ]:
print ( i )
x, y = 2, 9
if ( x > y ):
z = x - y
elif:
z = x + y
else:
z = 0
def function_p ( *args ):
numargs = len ( args )
if numargs < 1: raise TypeError ( "requires at least one argument" )
elif numargs == 1: pass
else: raise TypeError ( "Too many arguments" )
## Nah, Python does not have switch-case statement like Java
## Python short-circuit logical AND
## Python does not have logical "&&"
if True and True:
print ( "It is true!" )
a = ord('a')
b = 15
c = 0xf
d = 0b1111
print (a)
print (b)
print (c)
print (d)
print (hex(b))
print (bin(b))
#!/usr/bin/python3
#
# Python Template
#
def main():
print ("Hello World!")
if __name__ == "__main__"
main()
#!/usr/bin/python3
#
# Python Template
#
def main():
print "Hello World!"
if __name__ == "__main__"
main()
# Example variables
p, q = 10, 20
t = True
f = False
s = "a string"
d = 33.567
x = 123
y = 456
def function_a():
global y
x = 987
y = "banana"
print ( x )
function_a()
print ( x )
print ( y )
del x ## remove a variable and undefine it
# Example conditionals
if True:
print ( "It is true!" )
if i in [ 1,2,3 ]:
print ( i )
x, y = 2, 9
if ( x > y ):
z = x - y
elif:
z = x + y
else:
z = 0
# Example loops
for i in range(100):
print ( i )
days = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" ]
for d in days:
print ( d )
while True:
print ("It is still going!")
## Ok, don't do this, this is an infinite loop!
## You just did!? just type [Ctrl-C], phew...
# Example functions
def function_q():
pass
def function_x( a,b ):
return a + b
def functiona( a, b=100 ):
c = a
for i in range( b ):
c += i
return c
def function_y( list=[] ):
pass
def function_z( hash={} ):
print ( "in function_z" )
## without return, function returns None
function_q()
function_x( 1,2 )
function_y()
function_z()
## Try these, can you guess what will be printed?
print (function_z())
print (function_z)
# Example x = 0 x = "string" x = True x = False print ( x )
# Example
a = 1
b = 2
s = "string"
print ( a )
print ( a,b )
print ( s )
print ( " The number is " + 123 ) ## Ding ding ding! Error!
## I know what you are thinking, "but this works in Java, right?"
# Example print ( " The number is " + str(123) ) ## You know what, this works too! I love python! print ( " The number is ", 123 )
# Example x = x + 1 x += 1 x -= 1 y = x // 3 y = x % 3 x *= y + z x = x * (y+z) x /= y + z x = x / (y+z)
x =+ 5 y =- 3
# Example
def main():
print ("Hello World!")
# Example
def main(): # this is the main function
print ("Hello World!") # this prints Hello World!
# Example
def main():
a = 1
b = 2
a + b ## this will not be printed
c = a + b
print ( "The result is", c )
print ( a,b,c )
print ("Hello World!")
# undefine a variable in real time
del c
We'll cover this later...
#!/usr/local/bin/python3
def main():
print ("Hello World!")
if __name__ == "__main__":
main()
## make sure you change the file to be executable in shell.
## % chmod +x hw.py
import this >>> 2+2 4 >>> print( "Hello World!" ) Hello World! >>> a = 1 >>> b = 2 >>> a+b 3 >>> exit() ## or key in Ctrl-D
python3 --version
https://www.python.org Click here to Start! Click the Downloads tab, and choose Python3 or Python2.
https://code.visualstudio.com Click here to Start!
https://www.jetbrains.com/idea/ Click here to Start!
https://www.activestate.com/komodo-edit/ Click here to Start!
https://www.anaconda.com/download/#macos/ Click here to Start!
Go to Apple Store and search for Xcode. The first application should be it!
print "Hello World!"
print ( "Hello World!" )
#include <stdio.h>
int main (void)
{
printf ("Hello World!\n");
return 0;
}
#include <iostream>
using namespace std;
int main (void)
{
cout << "Hello World!\n");
return 0;
}
public class HelloWorld {
public static void main (String[] args) {
System.out.println ("Hello, World!");
}
}