String formatting¶

We have talked about strings before, and you know that it is possible to construct strings containing values, e.g.

In [ ]:
'x=' + str(43.2) + ', y=' + str(1./3.)


However, one may want to format the values in more detail, for example forcing values to be a certain length, or have a certain number of decimal places. This is called string formatting.

The syntax for formatting strings looks like this:

In [ ]:
"{0} {1} {2}".format(1./3., 2./7., 2.)


In the above example, the 0, 1, and 2 refer to the position of the argument in the parentheses, so one could also do:

In [ ]:
"{0} {0} {1}".format(1./3., 2./7.)


By default, the value looks the same as if one had used str(), but you can also specify the format and number of decimal places:

In [ ]:
"{0:10.3f}".format(1./3.)


The f stands for floating-point, the 10 is the total length of the string, and the 3 is the nuber of decimal places.

We can do something similar for integers (without the number of decimal places):

In [ ]:
"{0:10d}".format(4)


There are a number of options for string formatting - for instance, one can add leading zeros:

In [ ]:
"{0:010d}".format(4)


or align to the left:

In [ ]:
"{0:<10d}".format(4)


Instead of using 0, 1, etc. it is also possible to pass the values by name:

In [ ]:
"{day:02d}".format(day=3)


Here is an example of string formatting for a date:

In [ ]:
"{year:04d}{month:02d}{day:02d}".format(year=2013, month=7, day=8)


Exercise 1¶

Write a function that takes year, month, day, hour, minutes, and seconds and converts them to a string with format 2006-03-22 13:12:55:

In [ ]:
# your solution here


Exercise 2¶

Write a function that takes a string like 2006-03-22 13:12:55 and return the year, month, day, hour, minutes, and seconds as integers:

In [ ]:
# your solution here