CSC 498D Useful File Python- Summary

Python How to make a multiplication in Python >>> 2+3*4 14 How to print variables in python >>> name = “Andrew” >>> name Andrew How to concatenate and print >>> print “Hello”, name Hello Andrew How to create a list >>> names = [“Ben”,”Chen”,”Yaqin”] How to get the length of a list >>> len(names) 3 How to get an item from the list >>> names[0] ‘Ben’ How to get an item from the list using negative values >>> names[-1] ‘Yaqin’ How to use slice to get substring >>> smiles=”C(=N)(N)N.C(=O)(O)O” >>> smiles[1:5] (=N) >>> smiles[10:-4] C(=O) How to find the location of an element >>> smiles.find(“(O”)) 15 >>> smiles.find(“.”) 9 >>> smiles.find(“.”,10) -1 #nt found >>> smiles.split(“.”) [‘C(=N)(N)N’,’C(=O)(O)O’] How to check if a string is inside another if “Br” in “Brother”: print “contains brother” Remove whitespace like chomp >>> line ‘ This is a comment \n” >>> line.strip() ‘This is a comment line’ Check if a string starts with >>> email = ‘ceorge@hotmail.com’ >>> email.startswith(“c”) True Check if string ends with >>> email = ‘ceorge@hotmail.com’ >>> email.startswith(“m”) False Turns list into string >>> names =[“Ben”,”Chen”,”Yaqin”] >>> “,” .join(names) ‘Ben , Chen, Yaqin’ Turn a string into upper case >>> “chen”.upper() CHEN Change the char of a string >>> s = “andrew” >>> s[0] = “A” #Doesn’t work >>> s = “A” + s[1:] >>> s Andrew Append element to a list >>> ids = [“9pti”,”2plv”,”1crn”] >>> ids.append(“1alm”) >>> ids [‘9pti’,’2plv,’1crn’,’1alm’] Delete element from list >>> del ids[0] >>> ids [‘2plv’,’1crn’,’1alm’] Sort elements from list >>> ids.sort() >>> ids [‘1alm’,’1crn’,’2plv’] Reverse elements from list >>> ids.reverse() >>> ids [‘2plv’,’1crn’,’1alm’] Insert element to list at a specific location >>> ids.insert(0,”9pti”) >>> ids [‘9pti,’2plv’,’1crn’,’1alm’] Zipping lists together >>> names [‘ben’,’chen’,’yaqin’] >>> gender = [0,0,1] >>> zip(names, gender) [(‘ben,0),(‘chen’,0),(‘yaqin,1)] How to create a dictionary (hash) in python symbol_to_name = { “H”: “Hydrogen”, “He”: “Helium”, “Li”: “Lithium”, “C”: “Carbon”, “O”: “Oxygen”, “N”: “Nitrogen” } How to get a value of a given key of a dictionary >>> Symbol_to_name[“C”] ‘carbon’ How to check if a value of a given key of a dictionary exists >>> “O” in symbol_to_name True >>> “U” in symbol_to_name False How to list all the keys of a given dictionary >>> symbol_to_name.keys() [‘C’,’H’,’O’,’N’,’Li’,’He] How to list all the values of a given dictionary >>> symbol_to_name.values() [‘carbon’, ‘hydrogen’,’oxygen’,’nitrogen’,’lithium’,’helium’] How to update a value from a given dictionary >>> symbol_to_name.update({“P”:”phosphorous”,”S”: “sulfut”}) How to print keys and values of a given dictionary >>> symbol_to_name.items() [(‘C’, ‘carbon’),( ‘H’, ‘hydrogen’),(‘O’,’oxygen’),(’N’, nitrogen’),(‘L’, ’lithium’),(‘H’, ’helium’)] How to delete a key of a given dictionary del symbol_to_name[‘C’] [( ‘H’, ‘hydrogen’),(‘O’,’oxygen’),(’N’, nitrogen’),(‘L’, ’lithium’),(‘H’, ’helium’)] How to use bool in python >>> smiles =”Hello world!” >>> bool(smiles) True >>> not bool(smiles) False How to use if in python >>> if not smiles print “The SMILES string is empty” How to use elif in python Mode =”absolute” If mode = “canonical”: smiles = “canonical” elif mode ==” simoeric”: else: do it. >>> smiles ‘absolute’ How to use For in python >>> names = [“Ben”,”Chen”,”Yaqin”] >>> for ame in names: print name Ben Chen Yaqin How to assign tuple in for loops Data = [ (“C20H2003”,”308.371”), (“C20H200k”,”316.393”), (“C20H200i”,”416.6”)] for (formula, mw) in data: print “The molecular weight of %s is %s” % (formula, mw) The molecular weight of C20H2003 is 308.371. The molecular weight of C20H200k is 316.393. The molecular weight of C20H200i is 416. 6. Break, continue Break: stop the for loop Continue: stop the current for loop and restart How to use range >>> range(5) [0,1,2,3,4] range(5,10) [5,6,7,8,9] range(0,10,2) [0,2,4,6,8] How to read a file >>> f = open(“names.txt”) >>> f.readline() Yaqin\n How to create file output in python Input_file = open(“in.txt”) Output_file = open(“out.txt,”w”) for line in input_file: output_file.write(line) Common file read/write: “w”: write mode “a”: append mode “wb”: write in binary” “r”: read mode (default) “rb”: “read in binary” “U” = “read files with Unix” Math: >>> import math >>> math.pi 3.14234234234234 >>> math.cos(0) 1.0 >>> math.cos(math.pi) -1.0 >>> dir(math) [‘doc’os…..] >>> help(math) >>> help (math.cos)