CHEAT SHEET 7

 For Loop Over a Function

Note that using loops, you can call any function multiple times, even your own functions. Let's suppose we defined this function:

def celsius_to_kelvin(cels):
    return cels + 273.15

That is a function that gets a number as input, adds 273.15 to it and returns the result. A for loop allows us to execute that function over a list of numbers:

monday_temperatures = [9.1, 8.8, -270.15]
 
for temperature in monday_temperatures:
    print(celsius_to_kelvin(temperature))

The output of that would be:

282.25
281.95
3.0

So, in the first iteration celsius_to_kelvin(9.1) was executed, in the second celsius_to_kelvin(8.8) and in the third celsius_to_kelvin(-270.15).

That's just something to keep in mind.

Bonus Code: Dictionary Loop and String Formatting

You can combine a dictionary for loop with string formatting to create text containing information from the dictionary:

phone_numbers = {"John Smith": "+37682929928", "Marry Simpons": "+423998200919"}
 
for pair in phone_numbers.items():
    print("{} has as phone number {}".format(pair[0], pair[1]))

Another (better) way to do it::

phone_numbers = {"John Smith": "+37682929928", "Marry Simpons": "+423998200919"}
 
for key, value in phone_numbers.items():
    print("{} has as phone number {}".format(key, value))

In both cases the output is:

Output:

John Smith has as phone number +37682929928

Marry Simpons has as phone number +423998200919  

Cheatsheet (Loops)

In this section, you learned that:

• For loops are useful for executing a command over a large number of items.

• You can create a for loop like so:

for letter in 'abc':
    print(letter.upper())

Output:

A
B
C

• The name after for (e.g. letter) is just a variable name

  
  

• You can loop over dictionary keys:

phone_numbers = {"John Smith":"+37682929928","Marry Simpons":"+423998200919"}
for value in phone_numbers.keys():
    print(value)

Output:

John Smith
Marry Simpsons

• You can loop over dictionary values:

phone_numbers = {"John Smith":"+37682929928","Marry Simpons":"+423998200919"}
for value in phone_numbers.values():
    print(value)

Output:

+37682929928
+423998200919

• You can loop over dictionary items:

  phone_numbers = {"John Smith":"+37682929928","Marry Simpons":"+423998200919"}
  for key, value in phone_numbers.items():
      print(key, value)

  Output: 

  ('John Smith', '+37682929928')

  ('Marry Simpons', '+423998200919')

• While loops will run as long as a condition is true:

  while datetime.datetime.now() < datetime.datetime(2090, 8, 20, 19, 30, 20):
      print("It's not yet 19:30:20 of 2090.8.20")

  The loop above will print out the string inside print() over and over again until the 20th of August, 2090.

PYTHON PROGRAM SYNTAX SERIES