C02_Functions_EmilyVonAldenbruck

Language Semantics

The Python language design is distinguished by its emphasis on readability, simplicity, and explicitness

Indention and not Braces

Python uses whitespace (tabs or spaces) to structure code instead of using braces as in many other languages like R, C++, Java, and Perl. A colon denotes the start of an indented code block after which all of the code must be indented by the same amount until the end of the block

less= [] greater=[] for x in [1, 2, 3, 4, 8, 6]: if x < 3: less.append(x) else: greater.append(x) print("less=",less,"greater=",greater)

Variables and Arguments Passing

When assigning a variable (or name) in Python, you are creating a reference to the object shown on the righthand side of the equals sign. Consider a list of integers.

a = [1,2,3,] a

b=a b

In some languages, the assignment of b will cause the data [1, 2, 3] to be copied. In Python, a and b actually now refer to the same object, the original list [1, 2, 3]

a.append(4) b

Python has several built-in keywords for conditional logic, loops, and other standard control flow concepts found in other programming languages.

If, elif, else

The if statement is one of the most well-known control flow statement types. It checks a condition that, if True, evaluates the code in the block that follows

x= -5 if x<0: print("It's negative")

An if statement can be optionally followed by one or more elif blocks and a catchall else block if all of the conditions are False

print(x) if int(x) < 0: print("It's negative") elif int(x) == 0: print("Equal to zero") elif 0 < int(x) < 5: print("Positive but smaller than 5") else: print("Positive and larger than or equal to 5")

for loops are for iterating over a collection (like a list or tuple) or an iterater. The standard syntax for a for loop is:

for value in collection: do something with value

sequence= [ 1, 2, 0, 4, 6, 5, 2, 1] total=0 for value in sequence: total +=value # total =total + value print("total=",total)

sequence = [1,2,None,4,None,5] total=0 for value in sequence: if value is None: continue total+=value print(total)

sequence = [1, 2, 0, 4, 6, 5, 2, 1] total_until_5 = 0 for value in sequence: if value == 5: break total_until_5 += value print(total_until_5)

for i in range (4): for j in range (4): if j >i: break print ((i, j))

While Loop

A while loop specifies a condition and a block of code that is to be executed until the condition evaluates to False or the loop is explicitly ended with break

x=256 total=0 while x>0: print(x) if total >500: break total += x print(total) x //=2

x=0 if x<0: print("negative!") elif x==0: print("Zero") pass else: print("positive!")

Range

seq = [10, 20, 30, 40 ] for i in range (len(seq)): print("element %d: %d"%(i, seq[i]))

Enumerate

%formatting %d - integer %g - scientific %f - floating number %0.2f - 2 decimal places %s - string

# enumerate function l1 = ["eat", "sleep", "repeat"] # creating enumerate objects obj1 = enumerate(l1) print ("Return type:", type(obj1)) print (list(enumerate(l1)))

Sorted

a= [7, 1, 2, 6, 0, 3, 2] sorted(a)

print(sorted("COP2000 Python Programming"))

Zip

seq1 =["Un", "Dos", "Tres"] seq2 = ["one", "two", "three"] zipped=zip(seq1,seq2) list(zipped)

seq3= [False, True] list(zip(seq1, seq2,seq3))

for index, (a, b) in enumerate(zip(seq1, seq2)): print(f"{index}:{a},{b}") # https://realpython.com/python-f-strings/

Reversed

list(reversed(range(10)))

def apply_to_list(some_list,f): return[f(x) for x in some_list] ints = [2,4,6,8,1,3,5] apply_to_list(ints,lambda x: x**2)

! wget "https://www.gutenberg.org/files/76/76-0.txt" -O adventures.txt ! ( head -10 adventures.txt) > adventures10.txt

f = open("adventures10.txt", encoding="utf-8") for line in f: print(line)