Kategorie: Daily Code

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