Kategorie: Basics

 

We read a .png file:

 

The Image:

 

The code:

 

# Read binary files
binf = open("test.png", "rb")
print(binf.read())

The output:

 

# Read and write files

# open the file with 'write'-mode
test_file = open("files_test.txt", "r")


# full list of file modes
# "w" - write text file (overwrite possible)
# "r" - read text file
# 'x' - write text file (includes error is file exists)
# 'a' - append to end of file
# 'rb' - read binary files
# 'wb' - write binary
# 'w+b' - read and write binary file
# 'xb' - write binary file (includes error is file exists)
# 'ab' - append to end of binary file

# Read files
print(test_file.read())                     # This is a test - full text

# Read one line
print(test_file.readline())                  # This is a test - one line


# iterate over text files
for line in test_file:
    print(line)                              # This is a test - all lines

# readline() is not very well suited to iterate over big files

# close files - you should alway close a file after using it!!!
test_file.close()

# Write to files
texty = open("files_test.txt", 'w')
texty.write("11 This is a test\n")
print(texty.read())
texty.close()

# Indexing
# note: sets can't be indexed

my_guitars = ["Gibson Les Paul", "Ibanez RG", "Fender Stratocaster"]

print(my_guitars[0])                # Gibson Les Paul

# Python allows negative indexing. -1 returns the last item aso
print(my_guitars[-1])               # Fender Stratocaster
print(my_guitars[-2])               # Ibanez RG


# indexing a tuple
print(("Marshall", "Laney", "Orange")[1])       # Laney

# indexing a string
print("Wampler"[3])                 # p - index starts at 0

# slicing
print(my_guitars[0:2])              # ['Gibson Les Paul', 'Ibanez RG']


# note: the first index is optional. negative indexing works here as well
print(my_guitars[:2])              # ['Gibson Les Paul', 'Ibanez RG']
print(my_guitars[:-1])              # ['Gibson Les Paul', 'Ibanez RG']


#Examples

# get first and last letter
name = "Robert"

print(name[0])                      # R
print(name[-1])                     # t

# delete the file extension
filename = "document.txt"

print(filename[0:-4])               # document

# Functions

# declaring a Function
# if there is no return in the Functions
# python will return the last command line

def func(para1, para2):
    ''' explain what happens here '''
    sum  = para1 + para2                # variables declared inside functions are local
    return sum

#calling a function
sum = func(13,5)               # 18 this sum is not related to the sum-variable in the function
print(sum)


#using default parameters
def def_func(x, y=3):          # y=3 is a default parameter
    return x + y

print(def_func(2))             # 5 - the function will use the default parameter

print(def_func(5,8))           # 13 - default parameters can be overwritten


# Examples:

def is_odd(num):
    ''' returns true if number is odd '''
    if (num % 2 == 0):
        return True
    else:
        return False

print(is_odd(4))                                    # True


def is_prime(x):
    ''' checks if number is prime '''
    ''' only natural number bigger 1 can be considered primes '''
    if (x > 1):
        return all(x % i for i in range(2, x))
    else:
        return False                                # if number is 1 or less

print(is_prime(3))                                  # True

# dictionaries
import collections
# creating a dictionary
data = {"first" : "Linus", "last" : "of Paros"}

# add keys and values
data["age"] = 3
data["job"] = "Dog"

print(data)                     # {'first': 'Linus', 'last': 'of Paros', 'age': 3, 'job': 'Dog'}

#retrieving values
print(data["first"])            # Linus

print(data["first"] + " " + data["last"] + " is a " + data["job"] ) # Linus of Paros is a Dog

# check if a key is in the dict with in operator
print("first" in data)          # True
print("car" in data)            # False

# with get you can set a default in case a key is not found in a dict
shortcut = data.get("address", "unknown")

print(shortcut)                 # unknown

# remove keys and values
numbers = {"1" : "true", "2" : "false","2" : "false", "3" : "true"}

del numbers["2"]

print(numbers)                  # {'1': 'true', '3': 'true'}

# iterating over dictionaries
age = {"Don" : 55, "Cindy" : 52, "James" : 42, "Sara" : 35}

for name in age:
    print(name)                 # Don, Cindy, James, Sara

for name in age.values():
    print(name)                 # 55, 52, 42, 35

# Iteration examples

# get the average length of items in the list
list = ["Sara", "Christiano", "Dorothy", "Pete", "Peter"]
list.append("Robert")
average = 0

for name in list:
    average += len(name)                 # adds the length of every item to average

average_length = average / len(list)
print("The average length is: " + str(average_length))      #   ...length is: 6.0

# find an item in list
if "Sara" in list:
    print("found Sara")                 # found Sara
else:
    print("Not found")

if "Tucker" in list:
    print("found Tucker")
else:
    print("Not found")                  # Not found

# iterating with while loops

n = 10
numb = []
while n > 0:
    numb.append(n)
    n -= 1

print(numb)                     # [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

# list - holds a list of objects
# can be of any type and mix them
# lists are mutable

names = []                      # create an empty list
names_1 = ["Harvey", "Charles"] # create a populated list

# with list a string will return as individual chars
custom_list = list("Robert")

print(custom_list)              # ['R', 'o', 'b', 'e', 'r', 't']

# get specific items with index (index starts at 0)
print(names_1[0])               # Harvey
print(names_1[1])               # Charles

#list insertion

#insert an item with index
names_1.insert(1, "Dave")
print(names_1)                  # ['Harvey', 'Dave', 'Charles']

#append an item at the end of the list
names_1.append("Clara")
print(names_1)                  # ['Harvey', 'Dave', 'Charles', 'Clara']

#replace an item with index
names_1[1] = "Sophie"
print(names_1)                  # ['Harvey', 'Sophie', 'Charles', 'Clara']

# delete an list item
#1
names_1.remove("Harvey")
print(names_1)                  # ['Sophie', 'Charles', 'Clara']

#2
del names_1[2]
print(names_1)                  # ['Sophie', 'Charles']

# sorting a list

# sort strings alphabetically
names_1.sort()
print(names_1)                  # ['Charles', 'Sophie']

# sort numbers
numbers = [3,2,7,-3,99]
print(numbers)                  # [3, 2, 7, -3, 99]

numbers.sort()
print(numbers)                  # [-3, 2, 3, 7, 99]

# ATTENTION: You can't sort numbers and strings in one list -> error

#example

# tuples - holds unmutable items
# tuples can't be changed
# tuples can serve as keys in dictionaries
# ideal for unchanging values like pi or 24 hours

# crate a tuple
tuple_name = ("Steven", "Alice", "Vincent")

print (tuple_name)

print(tuple_name[1])                # Alice

# cannot append to tuples

# Sets
# sets are mutable and don't care about order
# they are great to check membership, remove duplicates and are hashable

digits = [0,1,1,2,3,4,4,5,6,7,8.5,9]

digit_set =  set(digits)        # removes duplicates

print(digit_set)                # Output: {0, 1, 2, 3, 4, 5, 6, 7, 8.5, 9}

print(9 in digit_set)           # True - checks if 9 is a member of the sets

# you can add or remove other Sets
even = {2,4,6,8,10}                # note we are using {} here instead of []

odd = digit_set - even              # remove even from digit_set

print(odd)                          # Output {0, 1, 3, 5, 7, 8.5, 9}

 

I am back – it’s been a week. It was an unplanned break since my son got a fever and than I got an unexpected job offer.

 

I own a very beautiful Gibson Les Paul guitar that I love very much. But the action – the distance between fret and string – is a bit too far off.

 

That is no problem because the Gibson website tells me exactly that the correct distance should be 3/64 inches! Ok. What?

 

First of all I am European. Inches are not unheard of and I know that one inch are 25.4 millimetres. But 3/64 inches? Come on!

 

Thank god for Python:

 

inches = "3/64"                                 # the inch value

slash_pos = inches.find("/") + 1                # look where the slash seperates the numbers

first_num = inches[0]                           # get the numerator
sec_num = inches[slash_pos:]                    # get the denominator

dec_inch = 1 / int(sec_num) * int(first_num)    # create a decimal inch value

get_mm = 25.4 * dec_inch                        # convert it to mm

print(inches + " inches are ""%.2f" % get_mm + " mm")  # round the float to to decimals


# Output: 3/64 inches are 1.19 mm

 

# Conditionals in Python:
# <         less than 
# >         greater than 
# <=        equal or less 
# >=        equal or greater
# ==        equal to
# !=        not equal to
# is        identical object
# is not    Not identical object


number = input("Enter a number: ")

if (int(number)%2 == 0):
    print("Number is even")
else:
    print("Number is odd")

# the conditionals 'is' and 'is not'
name_1 = "matt"
name_2 = "tim"
name_3 = name_1

if (name_1 is name_3):                  # statement is true
    print("The same object!")

if (name_1 is not name_2):              # this statement is also true
    print("Two different objects!")

score = 78

if (score > 90):
    grade = "A"
elif (score > 80):
    grade = "B"
elif (score > 70):
    grade = "C"
else:
    grade = "Failed"

print(grade)                        # C

# combining conditionals
name = "Duff"
gunsnroses = False

if (name == "axl" or
    name == "slash" or
    name == "Duff" or
    name == "steven" or
    name == "izzy"):
    gunsnroses = True
    print(gunsnroses)                           # true
else:
    gunsnroses = False
    print(gunsnroses)

# a more efficent way to do the above
gunner = False
gnr = {"Axl", "Duff", "Steven", "Izzy", "Slash"}
gunner = name in gnr

print(gunner)                                   # true