How
Contents
How#
How to write to a file#
To write to a file use open with the w parameter:
Tip
with open(filename, "w") as temporary_name:
...
For example, the following creates a file with the values of integer \(n\) and \(n^2\) on each row for \(1\leq n \leq 100\).
with open("squares.csv", "w") as f:
for n in range(1, 101):
f.write(f"{n}, {n ** 2}\n")
How to append to a file#
To write to a file without deleting what is already in the file use open with the a parameter:
Tip
with open(filename, "a") as temporary_name:
...
For example, the following appends integer \(n\) and \(n^2\) on each row for \(101\leq n \leq 200\).
with open("squares.csv", "a") as f:
for n in range(101, 201):
f.write(f"{n}, {n ** 2}\n")
How to read from a file#
To read a file use open with the r parameter:
Tip
with open(filename, "r") as temporary_name:
...
For example, the following reads the data from squares.csv.
with open("squares.csv", "r") as f:
data_as_string = f.read()
data_as_string
'1, 1\n2, 4\n3, 9\n4, 16\n5, 25\n6, 36\n7, 49\n8, 64\n9, 81\n10, 100\n11, 121\n12, 144\n13, 169\n14, 196\n15, 225\n16, 256\n17, 289\n18, 324\n19, 361\n20, 400\n21, 441\n22, 484\n23, 529\n24, 576\n25, 625\n26, 676\n27, 729\n28, 784\n29, 841\n30, 900\n31, 961\n32, 1024\n33, 1089\n34, 1156\n35, 1225\n36, 1296\n37, 1369\n38, 1444\n39, 1521\n40, 1600\n41, 1681\n42, 1764\n43, 1849\n44, 1936\n45, 2025\n46, 2116\n47, 2209\n48, 2304\n49, 2401\n50, 2500\n51, 2601\n52, 2704\n53, 2809\n54, 2916\n55, 3025\n56, 3136\n57, 3249\n58, 3364\n59, 3481\n60, 3600\n61, 3721\n62, 3844\n63, 3969\n64, 4096\n65, 4225\n66, 4356\n67, 4489\n68, 4624\n69, 4761\n70, 4900\n71, 5041\n72, 5184\n73, 5329\n74, 5476\n75, 5625\n76, 5776\n77, 5929\n78, 6084\n79, 6241\n80, 6400\n81, 6561\n82, 6724\n83, 6889\n84, 7056\n85, 7225\n86, 7396\n87, 7569\n88, 7744\n89, 7921\n90, 8100\n91, 8281\n92, 8464\n93, 8649\n94, 8836\n95, 9025\n96, 9216\n97, 9409\n98, 9604\n99, 9801\n100, 10000\n101, 10201\n102, 10404\n103, 10609\n104, 10816\n105, 11025\n106, 11236\n107, 11449\n108, 11664\n109, 11881\n110, 12100\n111, 12321\n112, 12544\n113, 12769\n114, 12996\n115, 13225\n116, 13456\n117, 13689\n118, 13924\n119, 14161\n120, 14400\n121, 14641\n122, 14884\n123, 15129\n124, 15376\n125, 15625\n126, 15876\n127, 16129\n128, 16384\n129, 16641\n130, 16900\n131, 17161\n132, 17424\n133, 17689\n134, 17956\n135, 18225\n136, 18496\n137, 18769\n138, 19044\n139, 19321\n140, 19600\n141, 19881\n142, 20164\n143, 20449\n144, 20736\n145, 21025\n146, 21316\n147, 21609\n148, 21904\n149, 22201\n150, 22500\n151, 22801\n152, 23104\n153, 23409\n154, 23716\n155, 24025\n156, 24336\n157, 24649\n158, 24964\n159, 25281\n160, 25600\n161, 25921\n162, 26244\n163, 26569\n164, 26896\n165, 27225\n166, 27556\n167, 27889\n168, 28224\n169, 28561\n170, 28900\n171, 29241\n172, 29584\n173, 29929\n174, 30276\n175, 30625\n176, 30976\n177, 31329\n178, 31684\n179, 32041\n180, 32400\n181, 32761\n182, 33124\n183, 33489\n184, 33856\n185, 34225\n186, 34596\n187, 34969\n188, 35344\n189, 35721\n190, 36100\n191, 36481\n192, 36864\n193, 37249\n194, 37636\n195, 38025\n196, 38416\n197, 38809\n198, 39204\n199, 39601\n200, 40000\n'
How to turn a string in to a list#
To split a string on a given character and turn it in to a list use the split
method:
Tip
string.split()
For example to convert the data_as_string variable to a list of string:
data = data_as_string.split("\n")
data
['1, 1',
'2, 4',
'3, 9',
'4, 16',
'5, 25',
'6, 36',
'7, 49',
'8, 64',
'9, 81',
'10, 100',
'11, 121',
'12, 144',
'13, 169',
'14, 196',
'15, 225',
'16, 256',
'17, 289',
'18, 324',
'19, 361',
'20, 400',
'21, 441',
'22, 484',
'23, 529',
'24, 576',
'25, 625',
'26, 676',
'27, 729',
'28, 784',
'29, 841',
'30, 900',
'31, 961',
'32, 1024',
'33, 1089',
'34, 1156',
'35, 1225',
'36, 1296',
'37, 1369',
'38, 1444',
'39, 1521',
'40, 1600',
'41, 1681',
'42, 1764',
'43, 1849',
'44, 1936',
'45, 2025',
'46, 2116',
'47, 2209',
'48, 2304',
'49, 2401',
'50, 2500',
'51, 2601',
'52, 2704',
'53, 2809',
'54, 2916',
'55, 3025',
'56, 3136',
'57, 3249',
'58, 3364',
'59, 3481',
'60, 3600',
'61, 3721',
'62, 3844',
'63, 3969',
'64, 4096',
'65, 4225',
'66, 4356',
'67, 4489',
'68, 4624',
'69, 4761',
'70, 4900',
'71, 5041',
'72, 5184',
'73, 5329',
'74, 5476',
'75, 5625',
'76, 5776',
'77, 5929',
'78, 6084',
'79, 6241',
'80, 6400',
'81, 6561',
'82, 6724',
'83, 6889',
'84, 7056',
'85, 7225',
'86, 7396',
'87, 7569',
'88, 7744',
'89, 7921',
'90, 8100',
'91, 8281',
'92, 8464',
'93, 8649',
'94, 8836',
'95, 9025',
'96, 9216',
'97, 9409',
'98, 9604',
'99, 9801',
'100, 10000',
'101, 10201',
'102, 10404',
'103, 10609',
'104, 10816',
'105, 11025',
'106, 11236',
'107, 11449',
'108, 11664',
'109, 11881',
'110, 12100',
'111, 12321',
'112, 12544',
'113, 12769',
'114, 12996',
'115, 13225',
'116, 13456',
'117, 13689',
'118, 13924',
'119, 14161',
'120, 14400',
'121, 14641',
'122, 14884',
'123, 15129',
'124, 15376',
'125, 15625',
'126, 15876',
'127, 16129',
'128, 16384',
'129, 16641',
'130, 16900',
'131, 17161',
'132, 17424',
'133, 17689',
'134, 17956',
'135, 18225',
'136, 18496',
'137, 18769',
'138, 19044',
'139, 19321',
'140, 19600',
'141, 19881',
'142, 20164',
'143, 20449',
'144, 20736',
'145, 21025',
'146, 21316',
'147, 21609',
'148, 21904',
'149, 22201',
'150, 22500',
'151, 22801',
'152, 23104',
'153, 23409',
'154, 23716',
'155, 24025',
'156, 24336',
'157, 24649',
'158, 24964',
'159, 25281',
'160, 25600',
'161, 25921',
'162, 26244',
'163, 26569',
'164, 26896',
'165, 27225',
'166, 27556',
'167, 27889',
'168, 28224',
'169, 28561',
'170, 28900',
'171, 29241',
'172, 29584',
'173, 29929',
'174, 30276',
'175, 30625',
'176, 30976',
'177, 31329',
'178, 31684',
'179, 32041',
'180, 32400',
'181, 32761',
'182, 33124',
'183, 33489',
'184, 33856',
'185, 34225',
'186, 34596',
'187, 34969',
'188, 35344',
'189, 35721',
'190, 36100',
'191, 36481',
'192, 36864',
'193, 37249',
'194, 37636',
'195, 38025',
'196, 38416',
'197, 38809',
'198, 39204',
'199, 39601',
'200, 40000',
'']
Note that the last element is an empty row.
We can use the split method on each element of the data splitting on the ,
and also convert the entries to an integer.
data = [[int(n) for n in row.split(",")] for row in data_as_string.split("\n")[:-1]]
data
[[1, 1],
[2, 4],
[3, 9],
[4, 16],
[5, 25],
[6, 36],
[7, 49],
[8, 64],
[9, 81],
[10, 100],
[11, 121],
[12, 144],
[13, 169],
[14, 196],
[15, 225],
[16, 256],
[17, 289],
[18, 324],
[19, 361],
[20, 400],
[21, 441],
[22, 484],
[23, 529],
[24, 576],
[25, 625],
[26, 676],
[27, 729],
[28, 784],
[29, 841],
[30, 900],
[31, 961],
[32, 1024],
[33, 1089],
[34, 1156],
[35, 1225],
[36, 1296],
[37, 1369],
[38, 1444],
[39, 1521],
[40, 1600],
[41, 1681],
[42, 1764],
[43, 1849],
[44, 1936],
[45, 2025],
[46, 2116],
[47, 2209],
[48, 2304],
[49, 2401],
[50, 2500],
[51, 2601],
[52, 2704],
[53, 2809],
[54, 2916],
[55, 3025],
[56, 3136],
[57, 3249],
[58, 3364],
[59, 3481],
[60, 3600],
[61, 3721],
[62, 3844],
[63, 3969],
[64, 4096],
[65, 4225],
[66, 4356],
[67, 4489],
[68, 4624],
[69, 4761],
[70, 4900],
[71, 5041],
[72, 5184],
[73, 5329],
[74, 5476],
[75, 5625],
[76, 5776],
[77, 5929],
[78, 6084],
[79, 6241],
[80, 6400],
[81, 6561],
[82, 6724],
[83, 6889],
[84, 7056],
[85, 7225],
[86, 7396],
[87, 7569],
[88, 7744],
[89, 7921],
[90, 8100],
[91, 8281],
[92, 8464],
[93, 8649],
[94, 8836],
[95, 9025],
[96, 9216],
[97, 9409],
[98, 9604],
[99, 9801],
[100, 10000],
[101, 10201],
[102, 10404],
[103, 10609],
[104, 10816],
[105, 11025],
[106, 11236],
[107, 11449],
[108, 11664],
[109, 11881],
[110, 12100],
[111, 12321],
[112, 12544],
[113, 12769],
[114, 12996],
[115, 13225],
[116, 13456],
[117, 13689],
[118, 13924],
[119, 14161],
[120, 14400],
[121, 14641],
[122, 14884],
[123, 15129],
[124, 15376],
[125, 15625],
[126, 15876],
[127, 16129],
[128, 16384],
[129, 16641],
[130, 16900],
[131, 17161],
[132, 17424],
[133, 17689],
[134, 17956],
[135, 18225],
[136, 18496],
[137, 18769],
[138, 19044],
[139, 19321],
[140, 19600],
[141, 19881],
[142, 20164],
[143, 20449],
[144, 20736],
[145, 21025],
[146, 21316],
[147, 21609],
[148, 21904],
[149, 22201],
[150, 22500],
[151, 22801],
[152, 23104],
[153, 23409],
[154, 23716],
[155, 24025],
[156, 24336],
[157, 24649],
[158, 24964],
[159, 25281],
[160, 25600],
[161, 25921],
[162, 26244],
[163, 26569],
[164, 26896],
[165, 27225],
[166, 27556],
[167, 27889],
[168, 28224],
[169, 28561],
[170, 28900],
[171, 29241],
[172, 29584],
[173, 29929],
[174, 30276],
[175, 30625],
[176, 30976],
[177, 31329],
[178, 31684],
[179, 32041],
[180, 32400],
[181, 32761],
[182, 33124],
[183, 33489],
[184, 33856],
[185, 34225],
[186, 34596],
[187, 34969],
[188, 35344],
[189, 35721],
[190, 36100],
[191, 36481],
[192, 36864],
[193, 37249],
[194, 37636],
[195, 38025],
[196, 38416],
[197, 38809],
[198, 39204],
[199, 39601],
[200, 40000]]