## Python Basics

The absolute basics:

Strings

```print("Goodbye, World!") x = "string value" print (x)```

Integers

```myint = 7 print(myint)```

Floats

```myfloat = 7.0 print(myfloat) myfloat = float(7) print(myfloat)```

Examples

```one = 1 two = 2 three = one + two print(three)```

```hello = "hello" world = "world" helloworld = hello + " " + world print(helloworld)```

Further Example

This one with a few conditionals involved

```mystring = "hello" myfloat = 10.0 myint = 20```

# testing code
```if mystring == "hello": print("String: %s" % mystring) if isinstance(myfloat, float) and myfloat == 10.0: print("Float: %f" % myfloat) if isinstance(myint, int) and myint == 20: print("Integer: %d" % myint)```

Lists and Iterating

```mylist = [] mylist.append(1) mylist.append(2) mylist.append(3) print(mylist) # prints 1 print(mylist) # prints 2 print(mylist) # prints 3```

# prints out 1,2,3
```for x in mylist: print(x)```

Example

```numbers = [1,2,3] strings = ["hello","world"] names = ["John", "Eric", "Jessica"]```

# write your code here
second_name = names

# this code should write out the filled arrays and the second name in the names list (Eric).
print(numbers)
print(strings)
print(“The second name on the names list is %s” % second_name)

Mathematical Operators and Ordering

Standard bodmas rules apply, and standard mathematic operators are used

 x + y x plus y x – y x minus y x * y x multiplied y x / y x divided by y x ** y x to the power of y

Strings & Formatting

Very C-like 🙂

``` # This prints out "Hello, John!" name = "John" print("Hello, %s!" % name)```

# This prints out “John is 23 years old.”
name = “John”
age = 23
print(“%s is %d years old.” % (name, age))

# This prints out “Hello John Doe. Your current balance is \$53.44.”
data = (“John”, “Doe”, 53.44)
format_string = “Hello %s %s. Your current balance is \$%s.”

print(format_string % data)

Many examples are mashed in here:

``` s = "Strings are awesome!" # Length should be 20 print("Length of s = %d" % len(s))```

# First occurrence of “a” should be at index 8
print(“The first occurrence of the letter a = %d” % s.index(“a”))

# Number of a’s should be 2
print(“a occurs %d times” % s.count(“a”))

# Slicing the string into bits
print(“The first five characters are ‘%s'” % s[:5]) # Start to 5
print(“The next five characters are ‘%s'” % s[5:10]) # 5 to 10
print(“The thirteenth character is ‘%s'” % s) # Just number 12
print(“The characters with odd index are ‘%s'” %s[1::2]) #(0-based indexing)
print(“The last five characters are ‘%s'” % s[-5:]) # 5th-from-last to end

# Convert everything to uppercase
print(“String in uppercase: %s” % s.upper())

# Convert everything to lowercase
print(“String in lowercase: %s” % s.lower())

# Check how a string starts
if s.startswith(“Str”):
print(“String starts with ‘Str’. Good!”)

# Check how a string ends
if s.endswith(“ome!”):
print(“String ends with ‘ome!’. Good!”)

# Split the string into three separate strings,
# each containing only a word
print(“Split the words of the string: %s” % s.split(” “))

Conditions and Boolean Operators

``` x = 2 name = "Rick" age = 23```

print(x == 2) # prints out True
print(x == 3) # prints out False
print(x < 3) # prints out True

``` if name == "John" and age == 23: print("Your name is John, and you are also 23 years old.")```

if name == “John”:
print(“Your name is John”)
else:
print(“Your name is not John”)

if name == “John” or name == “Rick”:
print(“Your name is either John or Rick.”)

x = 2
if x == 2:
print(“x equals two!”)
else:
print(“x does not equal to two.”)

Note: Python uses indentation to define codeblocks as seen in the above examples. Assuming they display properly – which they may not

The In Operator

``` name = "John" if name in ["John", "Rick"]: print("Your name is either John or Rick.") ```

The Not Operator

``` print(not False) # Prints out True ```

Loops

For Loop

``` primes = [2, 3, 5, 7] for prime in primes: print(prime)```

# Prints out the numbers 0,1,2,3,4
for x in range(5):
print(x)

# Prints out 3,4,5
for x in range(3, 6):
print(x)

# Prints out 3,5,7
for x in range(3, 8, 2):
print(x)

Clearly the arguments for this are (min, max, step)

While Loop

``` # Prints out 0,1,2,3,4```

count = 0
while count < 5:
print(count)
count += 1 # This is the same as count = count + 1

Break and Continue

``` # Prints out 0,1,2,3,4```

count = 0
while True:
# print(count)
count += 1
if count >= 5:
break

Break to exit the loop

``` # Prints out only odd numbers - 1,3,5,7,9 for x in range(10): # Check if x is even if x % 2 == 0: continue print(x) ```

Continue to move to the next statement, or codeblock

Else inside loops

``` #Prints out 0,1,2,3,4 and then it prints "count value reached 5"```

count=0

while(count<5):
print(count)
count +=1

else:
print(“count value reached %d” %(count))

# Prints out 1,2,3,4
for i in range(1, 10):
if(i%5==0):
break
print(i)
else:
print(“this is not printed because for loop is terminated because of break but not due to fail in condition”)

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