3.8 for Statement

• Repeat an action or several actions for each item in a sequence of items.
• A string is a sequence of individual characters.

for character in 'Programming':
    print(character, end='  ')

P  r  o  g  r  a  m  m  i  n  g  

• Upon entering the for loop, Python assigns the 'P' in 'Programming' to the target variable between keywords for and in.
• After executing the suite, Python assigns to character the next item in the sequence (that is, the 'r' in 'Programming'), then executes the suite again.
• Continues while there are more items in the sequence.
• Using the target variable in the suite is common but not required.

for Statement Flowchart

Function print’s end Keyword Argument

• print displays its argument(s), then moves the cursor to the next line.
• Can change this behavior with the argument end:

  print(character, end='  ')
  

• end is a keyword argument, but it's not a Python keyword.
• The Style Guide for Python Code recommends placing no spaces around a keyword argument’s =.
• Keyword arguments are sometimes called named arguments.

Function print’s sep Keyword Argument

• Keyword argument sep (short for separator) specifies the string that appears between the items that print displays.
• A space character by default.
• To remove the spaces, use an empty string with no characters between its quotes.

print(10, 20, 30, sep=', ')

10, 20, 30

3.8.1 Iterables, Lists and Iterators

• The sequence to the right of the for statement’s in keyword must be an iterable.
  • An object from which the for statement can take one item at a time.
• One of the most common iterables is a list, which is a comma-separated collection of items enclosed in square brackets ([ and ]).

total = 0

for number in [2, -3, 0, 17, 9]:
    total = total + number

total

25

• Each sequence has an iterator.
• The for statement uses the iterator “behind the scenes” to get each consecutive item until there are no more to process.

3.8.2 Built-In range Function and Generators

• Creates an iterable object that represents a sequence of consecutive integer values starting from 0 and continuing up to, but not including, the argument value.

for counter in range(10):
    print(counter, end=' ')

0 1 2 3 4 5 6 7 8 9 

Off-By-One Errors

A logic error known as an off-by-one error occurs when you assume that range’s argument value is included in the generated sequence.

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