Print

Print#

We’ve already been using print quite a bit, but now we’ll look at how to control how information is printed. Note that there is an older and newer way to format print statements – we’ll focus only on the newer way (it’s nicer).

This is compatible with both python 2 and 3

x = 1
y = 0.0000354
z = 3.0
s = "my string"

print(x)

We write a string with {} embedded to indicate where variables are to be inserted. Note that {} can take arguments. We use the format() method on the string to match the variables to the {}.

print("x = {}, y = {}, z = {}, s = {}".format(x, y, z, s))

x = 1, y = 3.54e-05, z = 3.0, s = my string

Before a semi-colon, we can give an optional index/position/descriptor of the value we want to print.

After the semi-colon we give a format specifier. It has a number field and a type, like f and g to describe how floating point numbers appear and how much precision to show. Other bits are possible as well (like justification).

print("x = {0}, y = {1:10.5g}, z = {2:.3f}, s = {3}".format(x, y, z, s))

x = 1, y =   3.54e-05, z = 3.000, s = my string

there are other formatting things, like justification, etc. See the tutorial

print("{:^80}".format("centered string"))

                                centered string

File I/O#

as expected, a file is an object. Here we’ll use the try, except block to capture exceptions (like if the file cannot be opened).

try: f = open("./sample.txt", "w")   # open for writing -- any file of the same name will be overwritten
except: 
    print("cannot open the file")

print(f)

<_io.TextIOWrapper name='./sample.txt' mode='w' encoding='UTF-8'>

f.write("this is my first write\n")
f.close()

we can easily loop over the lines in a file

try: 
    f = open("./test.txt", "r")
except:
    print("error: cannot open the file")
    
for line in f:
    print(line.split())
    
f.close()

['Lorem', 'ipsum', 'dolor', 'sit', 'amet,', 'consectetur', 'adipisicing', 'elit,', 'sed', 'do']
['eiusmod', 'tempor', 'incididunt', 'ut', 'labore', 'et', 'dolore', 'magna', 'aliqua.', 'Ut', 'enim', 'ad']
['minim', 'veniam,', 'quis', 'nostrud', 'exercitation', 'ullamco', 'laboris', 'nisi', 'ut']
['aliquip', 'ex', 'ea', 'commodo', 'consequat.', 'Duis', 'aute', 'irure', 'dolor', 'in']
['reprehenderit', 'in', 'voluptate', 'velit', 'esse', 'cillum', 'dolore', 'eu', 'fugiat', 'nulla']
['pariatur.', 'Excepteur', 'sint', 'occaecat', 'cupidatat', 'non', 'proident,', 'sunt', 'in']
['culpa', 'qui', 'officia', 'deserunt', 'mollit', 'anim', 'id', 'est', 'laborum.']
[]

as mentioned earlier, there are lots of string functions. Above we used strip() to remove the trailing whitespace and returns

CSV Files#

comma-separated values are an easy way to exchange data – you can generate these from a spreadsheet program. In the example below, we are assuming that the first line of the spreadsheet/csv file gives the headings that identify the columns.

Note that there is an amazing amount of variation in terms of what can be in a CSV file and what the format is – the csv module does a good job sorting this all out for you.

class Item(object):
    def __init__(self):
        self.name = ""
        self.quantity = 0
        self.unitprice = 0.0
        self.total = 0.0
    
import csv

reader = csv.reader(open("shopping.csv", "r"))

headings = None

shopping_list = []

for row in reader:
    if headings == None:
        # first row
        headings = row
    else:
        my_item = Item()
        my_item.name = row[headings.index("item")]
        my_item.quantity = row[headings.index("quantity")]
        my_item.unitprice = row[headings.index("unit price")]
        my_item.total = row[headings.index("total")]
        shopping_list.append(my_item)
    

for i in shopping_list:
    print ("item: {}, quantity: {}, unit price: {}, total: {}".format(i.name, i.quantity, i.unitprice, i.total))

item: apples, quantity: 2, unit price: 0.33, total: 0.66
item: bananas, quantity: 5, unit price: 0.1, total: 0.5
item: milk, quantity: 1, unit price: 2.5, total: 2.5
item: soda, quantity: 3, unit price: 1, total: 3
item: rolls, quantity: 12, unit price: 0.33, total: 3.96
item: eggs, quantity: 1, unit price: 2.5, total: 2.5

INI Files#

INI or Config files are a common way of specifying options to a program. They can take the form (from the ConfigParser page):

[My Section]
foodir: %(dir)s/whatever
dir=frob
long: this value continues
   in the next line

Here we look at how to read in options and store them in a dictionary of the form dict["sec.option"] = value

We’ll use a sample .ini file from a regression test suite (VARDEN-tests.ini)

(Note: the name of the module is ConfigParser in python 2 but configparser in python 3 – the latter confirms to the python style guidelines.)

import configparser

options = {}


cp = configparser.ConfigParser()
cp.optionxform = str    # this makes options case-sensitive
cp.read("VARDEN-tests.ini")

for sec in cp.sections():
    for opt in cp.options(sec):
        key = str(sec) + "." + str(opt)
        value = cp.get(sec,opt)
        options[key] = value
    
for k, v in options.items():
    print("{:32s}: {}".format(k, v))

main.boxLibDir                  : /home/regtester/RegTesting/BoxLib/
main.sourceDir                  : /home/regtester/RegTesting/VARDEN/
main.testTopDir                 : /home/regtester/RegTesting/rt-VARDEN/
main.webTopDir                  : /home/regtester/RegTesting/rt-VARDEN/web
main.compareToolDir             : /home/regtester/RegTesting/AmrPostprocessing/F_Src
main.MAKE                       : make
main.sourceTree                 : F_Src
main.numMakeJobs                : 8
main.COMP                       : g++
main.FCOMP                      : gfortran
main.suiteName                  : VARDEN
main.reportActiveTestsOnly      : 1
main.goUpLink                   : 1
main.MPIcommand                 : /usr/local/bin/mpiexec -n @nprocs@ @command@
main.MPIhost                    : 
bubble-2d.buildDir              : varden/test
bubble-2d.inputFile             : inputs_2d-regt
bubble-2d.dim                   : 2
bubble-2d.restartTest           : 0
bubble-2d.useMPI                : 1
bubble-2d.numprocs              : 2
bubble-2d.useOMP                : 0
bubble-2d.numthreads            : 2
bubble-2d.compileTest           : 0
bubble-2d.doVis                 : 0
bubble-3d.buildDir              : varden/test
bubble-3d.inputFile             : inputs_3d-regt
bubble-3d.dim                   : 3
bubble-3d.restartTest           : 0
bubble-3d.useMPI                : 1
bubble-3d.numprocs              : 3
bubble-3d.useOMP                : 1
bubble-3d.numthreads            : 2
bubble-3d.compileTest           : 0
bubble-3d.doVis                 : 0
bubble-restart.buildDir         : varden/test
bubble-restart.inputFile        : inputs-restart-regt
bubble-restart.dim              : 3
bubble-restart.restartTest      : 1
bubble-restart.restartFileNum   : 4
bubble-restart.useMPI           : 1
bubble-restart.numprocs         : 3
bubble-restart.useOMP           : 1
bubble-restart.numthreads       : 2
bubble-restart.compileTest      : 0
bubble-restart.doVis            : 0

Print

Contents

Print#

File I/O#

CSV Files#

INI Files#